If Brock wasn't against all the traveling, here's an idea I had for him (based on a dream about myself as a wrestler)
Basically, McMahon hires him back to shake up both Raw and Smackdown. So, insted of being aligned to one show or another, he can go to either show whenever he wants. Thus making him a kind of permanent free agent...goes on Raw some weeks, other weeks he's on Smackdown. That sort of thing.
Course, since the last time Brock left was because of all the traveling, I doubt WWE would do that with him.