This just an idea that I thought would be very cool:
You would choose a character and start playing as them when their powers first surface. So if you chose :iceman: you would start where the bully is attacking your girlfriend and then you would go through his life such when he goes to Professor X's school and when he became a Defender and you would learn different powers as he learns them.
There would be many X-Men to choose from and each would have a different storyline.
:btom: