You are conflating two separate issues.
Navi is an architecture not a specific GPU.

Evidence?

GDDR6 is in mass production.

They are going to have to eventually.

Indeed. Although I wouldn't be surprised if dev kits were floating about, it's far to early for a Playstation 5 or Xbox Two.

AMD has better, smaller, more efficient mobile CPU's though. In-fact, they even made a successor to Jaguar.

Your assertion is accurate up to a point.

Otherwise AMD would have made threadripper as one giant chip... But rather, that wasn't economic.
It was far more economical to use 8-core complexes stitched together as AMD could get more working chips per wafer that way.

Cell, Wii and Xenos say otherwise.

Flops isn't everything. Nor would it be achievable in the real world anyway.

Flops is a theoretical ceiling, often not achievable in the real world.
You can get that 8-9x increase in performance without an 8-9x increase in flops.

As for Ram, GDDR6 basically offers twice the performance/bandwidth over GDDR5. So 16GB of Ram should be the minimum I would expect.

No.

Having a zen based CPU is a certainty at this point.

Semi-Accurate don't always get everything right.

And nor should you take any outlet at face value because of a "track record". - You need to look at the evidence before forming an opinion.

Surely impossible now, very unlikely next year, but how about 2020? Don't forget that only the CPU should provide almost the same computing power also in undocked mode, while the GPU would run at a power considerably lower than in docked mode.  They could even include mobile and PC GPU cores and switch between them, the APU would cost more, but the hybrid model would be obviously priced higher than the base home-only one.
About Sony's will, who knows? Why shouldn't it want to take some portable market share back if it were possible? Obviously this would be viable if the market offered the needed power anyway, investing what's needed to make such devices just for PS5 would be a suicide. Thus it's just matter of launch date, for what regards feasibility. So yes, right now it's abstract reasoning, fantasy if you're just so eager to quickly dismiss it, but if feasibility arrives in time for next gen, why not? BTW it also depends on what Sony will be able to know about MS plans: if they include a hybrid, then it would be very likely that Sony wouldn't want to be the only one left without one. But neither Sony nor MS will let the competitors know it too early, so about this issue it will be a gamble for both, and this, again, makes not just feasibility, but also viability the decisive factors.

There's absolutely ZERO possibility it'll come out this year and the next. The PS4 is selling so well, releasing it before Q4 2020 would make absolutely no sense.

As for specs and hardware - that's anyone's guess. But don't expect anything crazy, Sony will want the launch price to be around $400/$450.

2020? still impossible... 

Why? well because the PS5 will be as powerful and as small as it can be and guess what, it will still be inside a box more or less the size of a PS4.

It will be absolutely as small and as power efficient as they can make it and still won't be enough to be a "portable" or "hybrid"

Sony is not chasing after Nintendo. Their customers expect top performance (for the price and console space) and any change to this philosophy would basically give out their market share to PC and whatever Microsoft will come up with next.

Sure the Switch niche is a nice one and I'm all for having a powerful handheld (still love and play my Vita till this day), but there is literally no chance Sony will handicap themselves chasing a fantasy and giving the ground to Microsoft in order to (maybe) make a more powerful switch. That would be Sony shooting themselves in the head.

To sum up, yes I'm quite convinced the leaks so far are probably real, yes we'll have a Ryzen - Navi based APU, we'll probably have GDDR6 and i'm quite convinced it will happen in the holiday of 2019. All depending on AMD having no more delays on their Navi architecture.

This does not mean that a few years later, and depending on Nintendo's continued success with the Switch, they couldn't release some sort of handheld that could basically play the same ps4/5 games on lower settings. This will not be the main PS5 SKU. I'll bet my left nut on it.

Nowhere I wrote that I think there wouldn't be full powered home versions, I definitely think that even taking ALSO the hybrid way, Sony would always offer powerful home-only versions too. As you wrote, and I forgot to mention, a huge factor would be the amount of success NS will enjoy in the longer term, right now it's just too early to say. But you also forget that current gen most powerful consoles, PS4 and XBOne, both use quite lightweight Jaguar CPU cores, so it will be quite easy for 2020 lightweight cores, based on Zen 2 or even Zen 3 architecture, to outperform them by a generation leap-worthy amount.
GPU is not a problem, as lightweight ones would be used only on hybrid units and maybe, with a more Sony-esque approach, even on them only when undocked, while home-consoles and docked hybrids could use beefier GPU cores, not to mention Premium versions that could use even stronger graphics units.
But all this requires time, surely it won't be viable next year even if it became feasible.
This is just a theory of mine, anyway, and it would make sense only in case the market will show that offering a hybrid version will become if not totally necessary, at least beneficial enough.
Maybe I wasn't clear enough before, but I agree with you that even with this strategy Sony should still offer full powered home-consoles too, its typical user base asks for them.

PlayStation would lose ALOT of their fanbase if they tried to mimic the Switch. And why should they? It's barely been out a year, it's far from being a proven handheld console.

In fact they shouldn't mimic it. Doing so would imply to launch ONLY a hybrid console, that would be totally against the PS phylosophy and it would do more harm than good, while what I suggest is to offer ALSO a hybrid version, and, as you correctly point out, if and only if the market will show that hybrids aren't a fad, hence the convenience, if current RAM prices and other factors weren't enough, to launch not earlier than in 2020. BTW, even launching in 2020, the hybrid version could be launched later, if the necessary chips aren't available or they're not cheap enough yet by the main launch date, the important thing is to decide and plan things when the time comes and then provide devs with the right dev kits, that's the most important thing, as adding portable features later would make costs grow for them. Anyhow, as I wrote in other posts, a hybrid choice NOW or in in 2019, even as just one of the units onoffered, is impossible for Sony,  current chips couldn't offer the generation performance leap Sony users expect,and high RAM prices would make very expensive to provide the right memory size to fully use the computing power available.
A later launch doesn't mean Sony would stand still in the meantime, as it could do another mid-late-gen step making the Pro the new PS4 base model and offering a new even more powerful Premium unit, and the new avaiolable computing power could be used not just for better graphics, but also to offer a more solid and enjoyable VR experience, so that when next gen comes, some more work would have been already done to make it more attractive for users, not to mention more testing done, more SW available and HW costs further driven down by a higher number of units already produced and sold to a higher number of early adopters.