Re: Wii Fit...
There is a ridiculous amount of martial arts simulation that the Wii could support.
Aikido-3D with Donovan Waite, anyone? Imagine instead of just watching it, being able to instantly see where and when your technique varies in path and pace. If they could re-do the motion capture and just put the remotes in his hands that is all they would essentially need to do for the core programming.
Iaido, Kyudo, heck, even Chado, though the heart of chado is serving others in the best form of hospitality. Well, make that one multiplayer then!