This has been bugging me for a while now. I know that the nunchuck add-on is usually used for character motion in a game. But what about the possibility of wireless footstraps that acting as the analog stick instead? I mean, it's not that hard to make. All you need is the motion sensors from the wii-mote (on the foot straps) and a wireless receiver (with the original nunchuck shoulder buttons on it) attached to the wii-mote in your hand, and you wouldn't even need a second controller port for this function.
In my dream-accessory scenario, there would be two foot straps per player. One is general movement (i.e. step forward a little to walk, step forward a lot to run, turn the foot to change directions, and sidestepping is possible too) and the other is there for a jump function (i.e. usually only the first strap leaves the ground as you move it around to control character movement, but if both straps leave the ground, the character would jump instead).
Possible uses for this kind of accessory would be:
RPG's and general exploration
Survival horror (jumping while playing used to make you look like an idiot or a wuss. Well, now jumping may save your life in the game.)
Platformers (Coin, coin, brick, brick... Mushroom!)
Sports games (like soccer and fighting as mentioned in another thread)
And of course... DDR
Sure, the incidents of Wii-related damages and injuries may increase, but I'd say that's a fair trade-off for an even more immersive gaming experience, right? :P