He's been at Apple before. Doubt he'll go back to a place he's been before unless he thinks the landscape has changed enough he can have a really big impact again. I don't think thats the case at 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.