A 4 core cpu would just not be good enough for next-gen system especially with 1 core being taken by the OS. If you wondering why exactly 7 cores instead of 8 cores it's cause it will be cheaper to produce with 1 core disabled.
Quad core CPU's have taken the role of the old dual-cores in terms of performance.
I.E. AMD's Ryzen's low-end are Quad-Cores.
Intels i3 is now Quad-Cores.
So it goes without saying... Regardless of the amount of cores that is chosen (8-Jaguar cores were roughly comparable to an Intel i3 Dual Core), having CPU performance around that level is probably something we might expect.
SMT (2 threads by core) is not ideal for a console, apparently it's kind of random. I think it would make much more sense (and be less expensive anyways) for 8 cores, 8 threads. Also BC with PS4 would be much easier like this.
The Xbox 360 had SMT, but it did bring with it some caveats that I won't get into here.
In short though, SMT would not prevent backwards compatibility, but when leveraged right can allow you to extract more performance out of each core.
AMD produce their CPU by chunk of 4. So it would be 6 cores (with 2 disabled) or 8.
Not even a factor when we start talking about monolithic semi-custom SoC's.
STORAGE: I believe the PS5 (and next Xbox) will finally jump to solid state drives. And of the M.2 variety. While the consoles will support PCIEx4 based nvMe drives by default (~2000Mb/s + reads) the consoles will come with a 1TB sata 3 based m.2 drive instead (~500Mb/s reads). Right now you can get a 512GB M.2 sata ssd for under $150.
Thats not what it would cost for sony and those prices will come down in the next 2/3yrs. Drives will be user upgradeable of course.
They will go with whatever is cheapest. - Even the Xbox One X isn't using the biggest, fastest mechanical disks and that was a "premium" console.
SSD's/m.2 drives still command a premium and will do so even in a few years from now.
Plus the demand for NAND is increasing, so costs could actually increase, especially if NAND fabs retool to start taking advantage of higher DRAM prices.
They almost have to with the PS4 Pro being so under powered compared to the Xbox One X. The One X is even out selling the Pro now, so most current owners don't even see the upgrade as being worth it. I tend to believe most of the rumors that the PS4 Pro will become the baseline PS4 and drop $299 the PS5 will be the "premium" console.
The Xbox One X outselling the Pro is an inconsequential issue as the Pro isn't the bulk of Playstation sales anyway.
As far as Ram, Maybe 16 Gigs of DDR5? Remember this thing has to be able to be priced at Sony's ideal price point of $399. I can't imagine that they want another PS3...
DDR5 isn't going to happen. JEDEC has only just finished demonstrating the DRAM and hasn't even finished ratifying the standard... And is thus probably still a few years away from a market release.
It does promise to double the bandwidth and density of DDR4, which means it's not going to be enough for next gen anyway unless you implement a stupidly wide bus.
It will be GDDR6, it will be what will offer the greatest benefits, higher capacities and good enough bandwidth/latency.
GDDR6 is currently ramping up production right now, so costs will be leveled out by the time 2020 hits.
But it proves that most PS4 owners don't deem it worth it to fork over 400 bucks to upgrade. New owners are still going with the base model. The Pro, unless it sees a price drop to $349 or even $299, sales will stay stagnant compared to the more powerful One X.
And didn't even know about GDDR6. In that case, I can't wait. As I stated though, don't expect to even hear about a PS5 until the PS4 hits 100 million which is easily doable at the end of this holiday season.
Remember when people said the no console would ever sell 100m again because of stupid mobile phones and tablets (which turned out to just be just a huge fad btw)? Aah, those were the days...