I think Nintendo will need all the money they can make. In developing the Wii replacement, I'd think they'd want and need to match the others and won't have the novelty advantage next time.
We have the Wii and 360 here and, no matter what, Wii is the hands down winner for family fun... and muscle pain. It also attracts people who don't normally play to at least try and they typically love it, too.
However, I wouldn't mind betting Microsoft is looking at some way to add this to the 360. The 360 lacks any really good kids or family type games. Still, if they could pull a controller system like Nintendo's out of their ass and use Live to feed out graphically less intensive type sports games. I think they'd be on a winner and it would be a fairly cost effective solution for them.
I love our Wii and the funtimes it's given us so far, but take out the fun factor of the control scheme and Golden Axe and it doesn't do a lot for me personally.