I think it's highly unlikely Microsoft will launch 2021. They will go 2020 as they don't want sony have a to big of a headstart.

The question is more if Sony launches 2019 or 2020 as both are an good option for them. If they launch 2019 they will probably have sold 10m+ consoles by the time Microsoft launch their console in 2020.

This gives Sony a big edge for the next generation of consoles.

I just wanna do a little post of both Sonys and Microsofts next console specs. The predictions are precise so we can see how wrong I will be :)

For PS5 sony will probably go for a similiar strategy as they did with Ps4 and Ps4 pro. A console in a small case, that's cheap to produce and the entire system pulls about 150W. This worked very well for them and they will probably stick to that strategy. For the Ps5 specs I got this:

Cpu: Ryzen 8/8 cores (no extra threads) with a clock speed of 2,6ghz. This will pull about 15-20W and zen2 is the most likely architecture.

Gpu: Navi 9,5 TF (upped the TF slightly from my last post). This should pull about 120W.

Memory: 16 GB ram, will be gddr6 with 448 GB/s of memory bandwidth.

Hard drive: 2 tb in memory storage. 140 mb/s read speed will be a laptop mechanical drive.

Release time: 2019 with a 449$ price tag.

For the Xbox two specs, it was a bit harder to speculate. As Microsoft has already released Xbox one X which is pretty powerful and it will be difficult to release a much better console with a mainstream price in 2020. They will probably aim to keep the title "The most powerful console", this is what I got:

Cpu: Ryzen 8/8 cores (no extra threads) with a clock speed of 3,2ghz. Will likely be zen2.

Gpu: Navi architecture with 13 TF of performance.

Memory: 12 GB gddr6 + 4gb ddr4. The operating system will run on the ddr4 ram and all the Gddr6 memory is for games. Microsoft will use a 384-bit bus width for increase memory bandwidth for an total 768 GB/s. (a bigger bus witdh is also a bit more expensive)

Hard drive: Mechanical desktop hard drive, 2 TB with 200 mb/s read speed.

Release time: 2020, 449$ price tag.

This console will be slightly more expensive to produce compared to the ps5 as the entire system will probably pull about 180-190W, it will require a bigger console case and a bigger fan.

Edit:

Both consoles will have backwards compatibility.

You are still looking at it wrong. The two primary benefits from doing a fabrication shrink are cramming more transistors in a similarly sized space and improved thermal efficiency. The latter means that it would be possible to clock the chip higher before hitting a thermal ceiling or as seen in tech these days, make the casing smaller and use a smaller fan or none at all. You get these by default, without even trying. 

So no, they wont double the compute cores in the XB1X (going from 40 to 80CU) then downclock it to 1050mhz. Thats counterproductive. At the very least it will run at the same clock or even higher. To not do so would mean that the console is prioritizing design over function. And thats just not how consoles are made. A 12TF GPU is pretty much they least you can expect on a 7nm process. 

Oh, the PS4 OG die size was 328mm2..... and it didn't have EsRam. The reason these are relevant is that it should give you an idea what die size the are already willing to hit while still remaining thermally stable without using any extreme cooling solutions. That should set the basis of what to expect from the next gen hardware. 

1. I have explained the GPU thing.
2. If using GDDR6 and 16GB of it, unless for some strange reason sony decides to underclock the Ram, or even crazier insist on using a smaller bus than the standard 256-bit bus in an attempt to bottle neck it..... then the least you will get is 500GB/s of bandwidth. And thats lowballing it.

Lol.... No. Look at it this way. This isn't another PS4pro to XB1X battle. Not a mid gen refresh. We are talking start of gen hardware here. There is not a chance in hell that MS lets sony release a new generation console a year earlier. Not a chance. Even with sony having won this gen, they would not let MS launch a year early either. And you really think sony will release in 2019, while bing the market leader and making a ton of money from the PS4 all the while launching a console that would have a GPU that is onna be as much as 3-4TF outpaced in as little as a year? Why?

Secondly, and more importantly..... if the PS4 and XB1 should have thought you anything, its that the next gen consoles will also be very similar in their hardware. More so next gen than they were this gen. Armed with that then you should know they are waiting for the exact same things before releasing their new hardware. 

Looking at the XB1X, and the fact that its more similar design wise to the OG PS4 than it is to the OG XB1, it should be relatively easy guessing exactly what to expect from the next gen consoles. 

My realistic, most likely scenario prediction for PlayStation 4 specs and a Fall 2019 release date:

• 7-nm GlobalFoundries or TSMC process
• Single-die APU style chip
• 8-core/16-thread AMD "Zen 2" cores (these cores are spec-complete & on track for release early 2019, according to AMD)
• *This would represent the same actual core count as PS4, but with VASTLY improved performance per core, plus a doubling overall of threads
• 64 CPU / 4096 Stream Processors GPU based on AMD "Navi" architecture
• *This would be a ~50% increase in shader unit count from the Xbox One X GPU - not too outrageous. Along with being an improved architecture overall, it should allow PS4 to hit native 4K in all titles with no issues.
• 16GB 16Gbps GDDR6 RAM, giving 512GB/sec memory bandwidth
• *These exact chips are already in mass production at Samsung for release later this year with discrete GPUs. So by fall 2019 prices should be easily mainstream enough for Sony to manage. 512GB/sec of bandwidth sounds like a lot, but really it's not a massive jump over the XBX's 326GB/sec
• 2TB 5400 RPM 2.5" Hard Disk Drive
• *Yes, another generation with a 5400 RPM laptop drive. SSD prices will still be too high to include a large enough drive. Considering how big games already are (nearly 100GB for GTA V now), by 2019 things will only be worse. 2TB is the MINIMUM that both Sony/MS should shoot for.
• Odds and ends: HDMI 2.1, Gigabit Ethernet, 802.11ac & 802.11ax Wi-Fi, Bluetooth 5
• *By fall 2019 all of these will be standard on every device, so I would hope Sony would include them...

And now for the DREAM PS5 specs (i.e. no chance of any of this happening but it would all be AVAILABLE to happen for either Sony or MS)

• 7-nm GlobalFoundries or TSMC process
• Two chips again, one discrete CPU and one discrete GPU, connected over AMD's InfinityFabric bus
• 16-core/32-thread AMD "Zen 2" CPU
• 8GB 2GBps HBM2 on 4096-bit bus, 1024GB/sec Memory Bandwidth attached to CPU
• 96 CU / 6144 Stream Processors GPU based on AMD "Navi" architecture
• 8GB 2GBps HBM2 on 4096-bit bus, 1024GB/sec Memory Bandwidth attached to GPU
• *Two chips means 2 pools of memory. However, I put the same type/speed on both in order to make it easy for the GPU to pool memory from the CPU if needed, and vice-versa.
• 512GB NVMe Solid State Drive + 2TB 5400 RPM HDD
• *The SSD would be built-into the motherboard and managed by Sony's OS as a permanent, insanely large cache. Whatever games you play most or have most recently downloaded would be put here, to optimize loading. The 2TB HDD would be where all of your data resides and still be user-upgradable.

I added my responses in the quote format. I don't know how to split up the quote format into smaller pieces.

Finally someone that made a prediction with worst specs than me :) thank you.

We have similiar prediction, except I think we will not see any extra cpu threads and that ps5 will have 4608 gpu cores or what you call them "stream processors". You made a very good prediction.

 The thing about your GPU prediction, is that as I have tried many times to point out it just doesn't make sense. Switching from 16nm to 7nm will mark a new generation of hardware all round. Even for AMD. A 64CU GPU will pretty much mark old gen tech in 2020. I mean just look at the og PS4. Going from 28nm to 16nm allowed them literally double the amount of CUs in the hardware. Literally double. And then upclocked it on top of that.

Now even if we are using the PS4pro as the new base (worst case scenario) we still end up with something that has 72CU (4608 stream processors). Now why they would do that when the same technology can be applied to the XB1X as a base is beyond me, and if they use the XB1X as a base then they end up with 80CU. Before any upclocking has been done.

All this is just doing the bare minimum that working with 7nm fabrication will allow. No envelopes have been pushed here. And if you think these all sound great? wait till you see whatever dedicated GPUs PCs will be using then. In comparison these will be lower level hardware.

They can try, but if they both release in the same year.... its unlikely. 

Sony didn't go with the fastest GDDR5 because the capacity they were using had just become available literally weeks before their PS4 unveil in feb 2013. Kinda like how Nvidias first batch of GDDR5x ram didnt go so well either.

And to hit over 500GB/s with GDDR6 over a 256-bit bus isn't even going with the fastest GDDR6. Its actually somewhere in the middle. Which is why I was saying that to go lower than that would be them going out of their way to do something they don't have to do. And don't forget, GDDR6 would be very mature technology by 2020.

Depends on your point of view. You could also say why didn't PS4 have 4.2TF and cost $600+ at launch (like PS3)? Pro could have been much more than 4.2TF in terms of available tech. Does that make them just good enough then, or does it make them a well rounded system that makes the best of all necessities, especially price? With tech performance continuing to slow, the more powerful the base console ends up, the harder the Pro sale becomes. It also depends on die size, space, cost, etc. If they decide to go with less CPU cores, that makes room for more GPU CU's, if they would rather spend more to have more. Also depends on if they want a $399 system or $499 system. Each gen the CPU/GPU tend to swap priority to some degree. I see PS5 focusing more on CPU.

A single large pool makes a lot of sense, but with Pro they decided to add a separate GB of DDR3, which doesn't really seem like enough to begin with, and strays from the PS4 single pool of RAM, so I dunno which way they will go. XB1X took full advantage of the RAM pool, but it also came at a price.

With some XB1X games at 4k coming in at 120GB, on board SSD or flash of around 200GB would be great if the game chosen to play could basically be transferred to the high speed storage. I don't see why they couldn't do this just like how downloads are done in a way that allows you to play quickly, without everything being loaded yet. Not sure how doable this is, but would be nice. Not sure if an SSHD would be beneficial in this scenario either, or if a typical HDD would end up performing similar. With external drives as an option, and slowly becoming the digital norm, while I have a hard time believing PS would go without mass storage altogether and leave it up to the customer (excluding on board), they could use a much smaller drive to save on costs.

I don't see the more expensive unit being the default happening this time. With PS4 and XB1, and now Pro and X, with sales still showing that clearly the base consoles are massively outselling the upgrades, you won't have that problem. Especially if there is a cheaper XB(1X) on the market, leaving consumers with the same two choices they had before from each brand. I also keep reading more and more in the comments and remarks sections, of people who say they really want to buy a Pro or X, but won't because they are afraid that next gen could come at any time. If PS5 and the Pro model both launched together, you wouldn't have this problem. You would have the problem of people wanting the Pro and not being able to afford it, but at least those same people can easily buy the base model, and upgrade later knowing they have at least 2 or 3 years before slims release, and 5 or 6 years before PS6 launches.

I dunno. A head start is a head start. If PS5 gets an entire years lead, and it's not a total disaster, XB 'Two' is going to have a really hard time gaining traction, unless it's a technical marvel, for super cheap, with an amazing games line up, which is a ridiculously tall order for XB in general, let alone by 2020. I remember reading a lot of people saying that they, or they thought, people would be super pissed off with mid gen consoles coming 3 or so years after this gens kick off. XB also has a record of 4/8 year gaps between launches, so 2021 fits the bill as of now. With XB1X hitting 6TF, the sooner they launch another upgrade, the less attractive it will be, or the more expensive it will be to make/sell. A beefy worthwhile XB"Two" most likely means subsidizing again.

1. I think even the base PS4 had a seperate pool of DDR3 ram. Though i think it was like 256MB or something like that. So really what we saw in the PS4pro is just a progression of that. It really comes down to what they intend to do with the system OS. If for some reason they decide to have as much as 8GB of system Ram, then in that case it would make more sense going for LPDDR4 ram as a seperate ram dedicated to the OS leaving the 16GB/20GB of GDDR6 ram untouched for games.
   
   
   
   
2. Well, Right now a 240GB SSD costs around $70 at retail. In 2020 it would probably cost around $50 at retail and for sony, soldering nand chips onto their MB (which costs even less than bulk ordering SSD drives) it would most likely cost them significantly less. So they could be spending like $20 or so for 200-256GB worth of nand flash storage. Another $20 for a 1/2TB mechanical drive. So its doable.
   
   
   Or the could spend like $40/$50 on what would amount to around 840GB/1TB of on board nand flash storage and forgo the mechanical drive completely  while still making room for the customer to put in there own HDD if they wanted or supporting external HDDs from day one. 

I would much rather see them go with 1TB of M.2 NVMe storage, with the ability for us to upgrade. I also think they should only support external SSD due to speed requirements. It will be a slight hit in 2020 or 2021, but SSD price will fall very fast and capacity will make leaps. If they don't stick it in, it opens the door to other companies to make much more capable boxes and have a generational leap over PS5 within a year or two of release.