Just my 2 cents.
PS4 at the moment is enjoying the throne for console gaming. They have 4k capability, great game lists, amazing gpu/cpu architecture. I don't see the need to push for PS5 when all the best technology is readily available. Of course there's plenty of new concept or existing ones that can be developed further, such as VR, AR, but its kinda risky to ditch the PS4 for something less enticing. 8k? perhaps, but how many has 8K tv? Its my hunch that Playstation might look into their handheld first instead of the console.

Having a great engine(graphics) but without good fuel(games) to run the car(gamers experience), it's only for decoration and bragging rights.