Quicksilver might be locked out by the X-men movie rights. I remember reading somewhere that he and Scarlet Witch were an odd gray area - they were more closely associated with the Avengers than the X-men so the characters aren't in Fox's license, but the whole mutant thing is, so if they did appear in the movies, they couldn't be mutants.
Could go with the joke cast on him. Tons of former action heroes getting silly parts these days. And to that end, with Disney owning both Marvel and Lucasfilm, the questionable status of the movie rights to Howard the Duck are resolved - whoever still holds it, they're all under one roof now. Give him Howard, and just to make it very clear he's being joke cast, have Tony build him the Iron Duck suit right before the climactic battle.
Well I can still see him playing Daredevil, nevermind that Ben played the role 1st. Even Iron Fist would be a good role, seeing how he uses martal arts too.
I can't picture it, actually i couldn't picture Affleck playing DD either till I saw him, and he did a wonderful job. IF the have to replace Affleck with a martial arts guy I think Jackie Chan would be a better choice.
If they are going to make changes to the Avengers I assume it will be to include another minority - Sam Jackson as Nick Fury isn't enough. They are going to need a Falcon, Rage, or Powerman/Luke Cage type.