With all the PS4 and PS4 Pro work that has been accomplished and it's implications for the PS5, there's no real reason to ditch AMD. Any PS5 devkit out in the wild is just going to be reflective of target specs at launch, of which a current 8 core Zen and probably a Vega 56 or 64 should cover. The new consoles are already hinged upon the availability of new memory foundries and 7nm, so until they are online and spitting out good yields, no new consoles. 2019 Is the absolute earliest to expect new systems I suspect, with 2020 being the more sensible year.
But how much memory will these new supposedly true 4K machines need? 16GB of HBM + 16GB of something less expensive?