I'd thought of an idea some years back, for a "Legion Academy" game. Various Legionnaires would serve as guest instructors, depending on what powers and skills you chose for your character. Expansion to a MMORPG level might be more tricky; as with any superhero-based game, there's only so many canon characters to go around. Not to mention the arguments about who can claim a popular character?
The solution I'd be looking at is sort of "LSH: The Next Generation". The United Planets, realizing how many worlds there are to cover, expand the Legion concept to a series of academies across their territory. The Legion worlds would be easy enough to depict, and some of the villains; new generations of Khunds and Dominators. Others you'd have to tweak; someone new can wield the Atomic Axe as the next Persuader, for example.