Wait, Nanoha is already the equivalent of Super Robot Wars.
But that would be the problem since that series probably has the most interesting abilities if it were to be a combat game. Well, it depends if you consider Mai-Hime to be a magical girl anime. Said game would be really colorful. But I have a bias towards platformers, if we're talking about that...
You'd have a lot of VA references, most definitely. One humorous one is probably Mami and Yuno or Homura and multiple characters (!) in Nanoha StrikerS
Nanoha probably needs a nerf. SLB's evolving from a bomb to a nuclear weapon as of late.