..............hmmmmmmmmm, a problem in the harsher sense of the word, I don't think so. But it's not hard to see that Marvel is going to wind up in a few predicaments with some actors and directors.
I think they have handled the most recent issues as well as they could have handled them--though I didn't really care for the Bruce Banner recast. Marvel is putting their characters first and foremost and they deserve a lot of credit for it.
That said, Marvel's plans are becoming one of the worst kept secret in Hollywood and anyone who wants in will have to accept the prospect of a incremental pay increase per sequel. Like it or not, take it or leave it. Part of me still doesn't like the problems this will create, but it emphasizes Marvel's commitment to their product. Honestly, it's inevitable that Marvel will eventually have to pony up big dollars and some point, be it to an actor or director. But the tone they set from the onset is very important. As some one else said earlier: "there are no sacred cows."
Look at it this way, how many A-listers are really going to sign on for these films anyway? The ones that do either don't mind (since money isn't a concern for them or the part is so small it doesn't garner a large payout) or they want to be part of something special and can see the big picture. These films are about the characters and not the actors so much--it's about the spectacle--putting your face in such a spectacle is like having a world wide advertisement. B to C listers will be more than willing, and A- listers who are on their way down the scale will or should be willing as well.
As for Favs wanting to do "other things", that shouldn't be any real surprise. Good film making is obviously a grind. Making good sequels is probably even more of a grind. Factor in expectations and the fact that like it or not, this is Marvel's baby and they are calling the shots in terms of where they want things to end up.........well, it is what it is. I still don't like it though, not letting a director complete his trilogy is usually a bad thing. Hate it actually as the vision may well become somewhat disjointed or inconsistent (x-franchise). But the Potter franchise has successfully done it without missing a beat or anyone noticing much of a difference in the quality of the films. That may very well be the approach Marvel has in mind for their films in general, should a director not want to finish what he started.
We have to remember, what Marvel is attempting has never been done before (though I believe Fox is the closest with their Predator and Alien franchises) and will garner more than it's fair share of criticism, skepticism, cheers and jeers. Actors and directors simply have to be aware of what they are getting themselves into. It's all about these characters first and foremost. These characters aren't theirs. PERIOD. If they cannot handle that,..........................
I think this is what has propelled the Potter franchise to it's current height, besides the books of course. Rowling had a huge say in how the films were done--she was not going to let some director's or actor's ego ruin her life's work. Frankly, you have to give Marvel a lot of credit for sticking to their guns so far--like it or not. Integrity of the party's involved with these types of films is usually sorely lacking and Marvel's steadfastness so far has garnered alot of respect amongst fans.