That would be cool, as long as they cast someone with great charisma like Chris Evans. This is the main reason i feel the whole Bucky Cap thing wont work. Because they havent really given us any personality, let alone a charismatic one, for Bucky. He would make a boring Captain America, potentially. Granted, they could probably change that... But... I'd rather just have them bring someone else in to play Steve Rogers I think.
Same with Falcon...to a lesser degree perhaps. We've seen Steve is the HEART of what Captain America is. He WAS Captain America even before he put on the suit. I dont see that with Bucky or Falcon...not without more of an "origin story" for those characters, which is now I little too late. They'd really have to SHOW themselves to BE Captain America at heart.
BUT... with the Infinity Gauntlet, I could also see somewhat of a soft reboot for characters/actors like Cap and Iron Man. Perhaps. Thus making a different actor a little more tolerable for some.