I'm not sure how they could introduce a more powerful PS4 and not totally fracture the user base. Perhaps PS5 with the same architecture as the PS4 with more powerful innards that could play any of the games that were on the PS4 would be nice, but I can't see that being popular enough to warrant trying to educate consumers on the differences of the two consoles. I mean, that's the tact that Nintendo seemingly tried with the Wii U and it hasn't worked out so hot for them.
Overall, it sounds like something that would be nice to have, but probably not financially viable for Sony. Either they'd have to sell it for too much or sell the PS4 for too little in order to justify it's existence. It would probably take me out of the console gaming market, also. I enjoy console exclusives here and there and it's nice to have access to them for years with just a single purchase, but if I needed to constantly upgrade to play them, I don't think I'd bother with it.