My guess is he is going back to Apple.
No - I think he'll go to Nvidia, because he hasn't been there before, hasn't really worked on GPU's before, and because I think GPU's could gain a lot of performance by having someone look at optimizing the big picture, adding the right abstraction layers, and generally making a GPU more CPU-like to allow more execution to be moved to it more easily.
He did two separate stints at AMD, and if the rumors of Apple switching the Mac to the A-series are true (which they probably are) then there will be some very interesting problems to solve over the next few years.