Earlier in the year, EA announced they'd bring a fight night game to the Wii. I think that may be the closest thing you're going to get for a while, because Nintendo doesn't really operate on common sense (ie., making games for the Wii that make you go "DUH....why'd it take you so long?").
Considering how well Wii Boxing works, I wouldn't be terribly excited about the prospect of another boxing game.
wii boxing is an awesome game. The controls get some getting used to and admittedly the game should maybe be a little more forthright on the how the game engine works (eg- doing sweeping punches), but ultimately, there is nothing in that game that I cant do. You have to remember that the controls do not just mimic the player. The game has strict rules and limits and you'll be punished if you step past them. eg, I've seen players just waving those things spastically fast, expecting the mii to do the same, which is stupid. You have to use controlled, well placed shots. Once you learn that you'll have a blast.