I think Quicksilver is a lock since the Flash was so awesome in the last game. Scarlet Witch probably will come with him.
Black Cat is also probably a lock (Lego Tits!!!)
I'm starting to think Falcon is more of a lock than Angel.
One none of us has mentioned yet, but is probably a lock is the Mandarin.
EDIT: Oh wait, Mandarin was on Natural's list. Never mind.