I would never use a custom soundtrack in Zelda, but perhaps some people would *shrug*
Really, custom soundtracks should work like it does in the 360; a standard system that's built into the console and can be used in every game. A firmware update can enable the Wii to do this. I don't know if it'd be usable in a preexisting game that's not coded to support the feature (it might be), but if it can't then just add the support for all future games. It'd be painfully easy to incorporate into a game, so why not?