As torok wrote in the second post of this thread, power whores hated last, very long generation during its last years, but it was a blessing for devs. This gen, with upgraded mid-gen units, can last as long or even longer and at the same time make also power whores happy again for some more years before they start asking again for a new gen.
So 2019-2021 is not an outlandish prediction.

And once again, everybody praise teh Almighty Analyst God!!!

I think when software sales start to dip, then a PS5 will come knocking around the door and until then, this gen will continue.

November 2019 or november 2020. PS4 is selling very well to Sony release a PS5 in 2018. And because PS4 Pro only has two month of release.

Still think people need to stop looking at PS4 as a console and start seeing it as an OS. The 4th generation PlayStation OS is very likely going to span over more than just the PS4 and PS4 Pro. I would not be surprised to see a PS4 Spec 3 that is slightly more porwerful than the PS4 Pro (maybe 8TF in 2018 with 12GB GDDR5) with PSVR tech and ports built in, and some form of Portable or mobile device as well. We may not see the PS5 OS and Hardware line for quite a while. My best guess for when we can see a true generational leap in CPU/GPU/RAM/Storage is 2022 - 2024.

It's not an OS. It's a "Platform". Playstation 4 and Playstation 4 are part of the same platform ecosystem.

PS4 and PS5 will most likely co-exist meaning PS5 could release in 2019/2020 while the PS4 is still selling until around 2022-2024. This all depends on sales of the PS4. Sales this year were down YOY even with the launch of the Slim and PRO. I'm not saying PS4's best years are behind it I'm just pointing out that PRO obviously didn't invigorate the sales enough to justify the thought that another upgrade is going to postpone the inevitable launch of the PS5.

I could see Sony releasing another Slim/PRO-II in 2018 or so but the PS5 will be the big leap in 2019 or 2020.

They just came off the largest quarter in the history of PlayStation. We have an incredible line-up of games coming out for PSVR and 4K HDR that will make PS4 Pro a very good buy over the next 12 months. I think we have to wait and see how things play out before we can fully say how the PS4 Pro is doing.

I fully expect a Slimmer Slim/Pro Slim when 7nm becomes available, the only question is if they will make PS5 at the time, or if they will continue to iterate on the PS4 hardware. Looking at where tech is, I don't see any chance of a console in 2019 - 2020 wowing people, and I think it would be bad for the industry to try and claim what they are offering is next gen. I think a 3rd PS4 revision that offers full 4K 30fps gameplay as a minimum is all they can achieve at that point. A true generational leap doesn't look possible until ~2023. That will be the point where they can deliver 4K graphics with massivly advanced rendering techniques. 

They may make PS5 for 2019 - 2020 with a ~12TFLOP APU, and 16GB HBM RAM, but I can't see it really capturing the market, because, it will not be able to wow people. It will just be a 4K PS4, and no where near the leap we saw from PS3 to PS4, which in itself was not nearly as impressive as PS2 to PS3. I just think we are better off polishing the current gen until a real leap can happen, to me that is the advantage Pro and Scorpio are offering us. They give us time until a real leap in computing can deliver a truly next level experience.

What's Packass saying now?! ('I don't see 4k broadcast until 2020')!!? Excuse me, Mr Packass. It's taken long enough to get to 1080i, what with the bandwidth issues. The only way people will get 4k broadcasts consistently is through streaming or physical formats, or paying extra for the premium sport channels. It certainly won't be mainstream across the board. 4k is a waste of time btw for people who don't like big screens (I'm a 40, maybe 43 inch fan). So count me out. And TV manufacturers should output HDR on 1080p teles, period! Otherwise they're taking the piss, cos not everyone's assed about 4k. I mean if people were that assed about high res they wouldn't bother with going to the cinema. 

Back on topic, there's no point sony releasing PS5 until it's twice the power of PS4 Pro. The performance gains otherwise won't be noticeable enough. At least 8 teraflops graphics on 10nm/7nm fab process.

Honestly even at 8 - 10 TFLOPS it is not really going to make a big difference. The difference between PS4 and PS5 just from a CPU/GPU standpoint would be about half the increase we have seen on every PS generation before. With deminishing returns, we don't need less improvement between generations, we need more. 8 - 10TFLOPS with 16GB of RAM would be a great 3rd generation PS4 though.

Well, if they go with a Vega 10 based card, we should see 11-12 Tflops.  The normal card is supposed to be 12.5, but I figure Sony will downclock it for heat reasons. If they can actually push the Vega 20 out in time, or Sony decides to use it even if it releases in early 2019 (which they may decide  to do, since prices should fall quickly after 6+ months) we could be seeing ~14-15 Tflops. Personally, I think they'll at least want to double the Scorpio, though, 2.5x would seem even more impressive.  Depending on which way they go, it'll be ~6x-8x more powerful than the OG PS4. And ~8x-11x more powerful than the OG XBO. I'd say that's a good leap.

As far as Scorpio comparisons go, it's also important to note that the games on the PS5 will blow away anything the Scorpio has, even if it's only 2x as powerful.  Reason being they won't be held back by a generation of HW. It'll also have GG and ND (possibly Kojima) exclusives that take full advantage of the HW, where the Scorpio is only getting ports from now on. Even MS games are going to be PC ports, most likely, as they are focusing on bringing PC gamers to their store.  Basically, games aren't going to be optimized much for it.  I think Sony's exclusives for PS4 probably see more optimization for the Pro than the Scorpio will see.

@ OP

I seriously doubt they will miss the 25th Anniversary of PS to release the PS5. The advertising is just too easy and writes itself. Either have the S backwards in PS5 to look like a 2 or have the S a backwards 2 to look like an S.  Even if it is released in 2020, it'll at least have an announcement for it on or around the 25th Anniversary.