Viability of a new portable PlayStation

That might work with a slight refocusing of PS+. Come the launch of the PS5, declare that anyone with a PS+ subscription can stream any purchased PS5 games on any compatible device: PC's, PS4's, and PS5's.

Keep PS+ at two games per month, one PS4, and one PS5. Streaming anything that you haven't purchased still requires PSNow.

 

It turns every PC/PS4 owning PS+ subscriber into the owner of an accessible PS5 library.

Digital PS5 purchases become more valuable, seeing as you can play them anywhere with a PC, PS4, or PS5, and don't have to wait for them to download.

PSNow gets advertised to every PS+ subscriber.

Hardware cost becomes less of a barrier to entry for the more casual audience, whilst the core audience will buy more expensive launch hardware. So we should see hardware somewhere on a scale of less subsidised to greater BoM.

Overall, Sony want more people buying into their subscriptions. Making PS+ a means of streaming your purchased PS5 games increases the value of both purchasing digital games and staying subscribed to PS+. Facilitating access to those services is largely determined by price point, which will be served well by a $250 PS4, $350 PS4Pro, and $450-500 PS5. But form factor matters too, as I think the Switch demonstrates.

R&D would probably be substantial and risky to create a whole new platform e.g. a more "Vita 2"-esque ARM device. It would be less risky to piggy back on R&D for the PS5 and its backwards compatibility. A Zen+Navi 7nm PS4 has a better ROI than the R&D required for porting Jaguar+Polaris to 7nm and beyond.

Slap a 10" screen and a battery pack on that Zen+Navi PS4 and you've got a portable. If the super slim PS4 has an external power supply, no ODD, and flash storage, it might even be suitable enough in its default form factor, with an optional, portable shell (my favourite.)

We might even get lucky and find the PS5's SSD tech being included for non-existent loading times!