I don't think they'd go for something completely new (save that for Wii3) but certainly a refinement of what they have. That would probably be even more immersive (with vitality sensors in the grip for instance) but at the same time, also more functional for more classic game types.
Motions & IR add a lot to certain game types - sandbox, FPS, adventure and sports but detract from or feel mimicky in others, esp: fighters (but then the wiimote is about accessiblity and when was SF ever accessible? My SFIV loving friend was over playing TvsC and while he admits it looks virtually as good and is as much fun to play he sneers at it's accessibility. Some games are not meant to be accessible, they are meant to be mastered by the very serious gamer)