This doesn't make sense to me/seems highly unlikely.
4k with modern games takes an extremely large amount of power to do while running games well. An upgraded PS4 like this would have to either be extremely expensive, run games really poorly, or simply not happen.
To put things in perspective, I have a $1300 gaming PC. It struggles to run some games at 1080p when at max settings (for example, Rise of the Tomb Raider). I've also tested some other things on it, like using the max AA settings on Final Fantasy Type 0 HD, which supersamples the game to 4k. My computer had framerate drops, and that's an HD remaster of a PSP game that runs at 30FPS normally. Because of my experience with 4k, I can't see how Sony could pull this off without having a PS4 that would be obscenely expensive. And at that point, would it really be worth it?