Let's go nuts. Motion controls for everything we can think of, in very cool and innovative ways. I have to stress cool and innovative. Imagine Con2 was all about motion controls. For the sake of this thread, assume the Wii can accurately capture your motion with no errors.
The SPAS' pump animation is rather slow... but if the game let you do a manual pump motion with both the nunchuck and wiimote it would speed it up. Sort of like an Active Reload of sorts but with the pump animation. It wouldn't be necessary; you could let the animation play out normally, but doing the pump motion yourself would just speed up your pump in-game.
In fact any reload could have some sort of Motion Active Reload that could speed up the reload or give some sort of other bonus like extended clips/magazines.
It'd also be cool to have different kinds of melee attacks depending on the motion you do: A thrust would have more range than any other attack but has the least damage, and it could be interrupted with firing the weapon for serious damage (if you can keep your reticule steady enough to actually hit your target). An uppercut motion would hit the enemy with the butt of the weapon and send them into the air to get some distance between the two of you. A swipe motion that's the fastest and, although not as powerful as the uppercut, still delivers a good amount of damage.
Rolling grenades! It'd be nice if you could roll grenades just by doing a "bowling" motion. Maps and some gaming mechanics could be built just for this (like curved surfaces or holes under some walls). If the game had doors, you'd be allowed to roll grenades under them even when closed.
There could also be an all-motion melee weapon. The fire/alt.fire/reload buttons might do stuff (like charging or shielding) or modify the weapon, but not attacking; that's for motion control.
What else? --- "A closet intellectual, he acts dumb to impress women." Daos (Doritos and Orange Soda) for Con2 currency name. I support this.