Firstly, cheers for the response!
Well, I'm bouncing around a few ideas (one of which was, in fact, an X-men inspired game, which I think is badass), but the main two going around my head are:
Wolfhearts: A game about young warriors and the tumultuous nature of young friendships (inspired by John Harper's the Wildlings)
and
Steelhearts: A game about samurai falling short of their ideals and the fallout that causes.
Particularly, with both these games, I'm really interested to see if I can get the AW/MH idea of limited or more specific moves to change the way the players view the narrarative in a different light. Wolfheart is about friendship and learning who you can trust and what happens when they trust is broken, while Steelhearts is about being in a vastly different sort of societal enviroment, and about emotional repression.
But damn, Mutanthearts, that's a fantastic name...
EDIT: Also, a Spy hack, I think. The dynamic shifts in power works perfectly for it, as well.