I think the way you should try to look at it is this, people know these characters (or at least they will after a second and third billion dollar Avengers film). They will practically be household names. Like Batman, Spider-Man and James Bond himself. By that time with all the complaints about "ugh another reboot, we've seen uncle ben die/batmans parents die/banner get blasted with gamma rays/etc a hundred times now!" At a certain point, people will know the characters well enough to not need reboots and will prefer recasts. So I'm not saying they should or shouldnt make these films indefinitely. I'm just saying the general audience will be the deciding factor. It all depends on how many viewers pay for what type of films. We, as comic book fans already know the characters. Iron Man is on the same level as Bond in my eyes. They did the origin story right once, watch RDJ do it if you want to experience it again. I, for one, am all for an indefinite series of films. Heck, didn't Iron Man's original series break 300 issues?