Re: Changing the roster for Avengers 2?
I don't think they're worried about them falling off the pop culture radar. They're probably looking to recast a good amount of them after A3 though. No way Evans is returning, that's the extent to which I see RDJ staying as Iron Man, and it's doubtful that Hemsworth and ScarJo return either. Sam Jackson's contract ends at A3 as well, but he's such a team player for this kind of stuff, I can see him resigning for more films.
So they'll possibly be replacing 6 members of the original cast after A3 (2018).