I was about to post this very question and then spotted someone else mention it in the Cena thread.
But you know it has to happen. Connery did six Bonds. RDJ has done three Iron Man, will have done 4 Avengers and some Spider-Man plus Cap: Civil War (not to mention Hulk cameo). He’ll be well in his fifties by the end of the decade and will be time to move on. Who can possibly replace him?
These movies make a billion dollars each so they’re not going to let them slip away. Like Bond, he’ll be replaced. But who can fill his shoes?
I think it needs to be an underdog with a chaotic personal life so people root for him like we rooted for RDJ. Sheen would have been perfect but maybe too old.