imagine if Sony releases a PlayStation 4K model which can play your PS4 games in either 1080p 60fps or in 4K 30fps.
It will cost 700$ to be realistic here. All current exclusive will be upated to run with the better performance like Bloodborne or Driveclub and future third party games would adapt it or allready patch their current games. But it would only support higher frame rate and resolutions but not graphics.
So it would be
400$ for PS4
700$ for PS4K
so everyone has the choice