Just a random exploration...
PS4 currently has ~270X level of performance [in reality it is bit below it because it has 2 less CUs and lower clocks, but architecture is the same]. This fits nicely with current state of things since PS4 is indeed there at 1080p30 in this particular game at great visual settings.
Now, if we can believe that Polaris is indeed 2.5x of the 28nm GCN, move to a 14nm APU would enable PS4K to remain at the same power level [even more if they adopt power levels of launch PS4] but gain tremendous rendering boost, more than FuryX! In this particular game it can achieve
~44fps at 4K when using good CPU [and no, we clearly don't need 4X GPU performance to jump from 1080p to 4K].
Of course, boosting GPU will help only in GPU-limited scenarios. To ensure that framerates go up for all games in all situations, they would need to boost CPU also. This is especially important for PSVR games that NEED to hit high [sometimes obscenely high] framerates, all the time.