I have done Wii Fit for a couple of weeks now. I really think Nintendo should expand this genre. Specifically, I think the engine could be expanded to practicing the piano fairly easily. I am not talking about Wii Music. I am talking about really practicing the piano.
There are two difficulties with bringing this game to reality. First, the player needs a piano. Second, the player needs to be able to see the screen while playing the piano.
My lack of creativity sees three basic ways to introduce a piano to the Wii. The first option is to sell a piano accessory. This option could not work because the piano would either be too flimsy or too expensive or (probably) both. Another option would be to have an accessory that plugs into digital pianos. This drastically reduces the audience, as not everybody has a digital piano. The final solution is the one I would suggest, which is to introduce a speaker accessory that can listen to whatever piano the players have. This actually seems like a realistic solution.
Dealing with the screen issue is more difficult. The easiest solution is to just make the screen unnecessary. Have instructions given through the accessory and teach piano via the Suzuki method. This basically eliminates a huge portion of the Wii experience, plus Suzuki is not as popular here in the US. This leaves two other options. Either force the piano to face the screen/TV (not always possible) or use a portable screen on the piano. The portable screen could be Wii specific or just a video transmission and receiving system.
I think something like this would have helped me be more excited about practicing the piano, at least for a couple of weeks.