By now most of us have probably heard the news that came out a couple of days ago about how when Robert Downey Jr tires of playing Tony Stark Marvel studios will just pull a James Bond and recast him. In my opinion this would be an absolutely horrible idea and would almost destroy everything the Cinematic universe has been to this point. This also shows the flaw with a Cinematic Universe. Unlike comics, the actors age and have other careers, they cant play them forever. And when the time comes when all of the Avengers have left their roles it will be much harder for them to recast or reboot because of how established the shared universe has become. The cinematic Universe cant pull off a recast like the old Batman movies did for example. Those movies shared certain elements but were all truly different takes on the character. So much so in fact that I have a hard time believing the Burton films and the Schuemaker films share a universe even though they shared an Alfred. In fact I truly believe that they dont. Even then when the two movies that for sure shared a universe (Forever and Batman and Robin) recast Batman it was absolutely terrible and neither audiences or critics could get behind it.
This universe that Marvel studios is creating is awesome and I cant wait to see how it progresses but it has a lifespan. Recasting characters has already happened in the universe with Rhodey and Bruce Banner. These recastings were huge sources of controversy and while I havent seen Ruffalos Banner, I personally cant take the new Rhodey as seriously as the old one, it just doesnt feel right and was one of my main problems with Iron Man 2. But with these two characters it was possible to recast without too much harm to the integrity of the Universe since Rhodey was a supporting character and Bruce Banner never really interacted with other major characters like Iron Man and Cap. However the second all these characters share the screen in the Avengers recasting them will be almost impossible to pull off. No one will buy a new Iron Man talking with the same Captain America and take it as seriously as they could have otherwise. It destroys the illusion of a shared universe.