I don't care how many consoles Wii sells, I don't think that motion controllers are going to make 27+ years of traditional controls obsolete in one generation, especially at their current level of functionality. I own a Wii, and I enjoy it, but if I had to give one of my systems up I'd choose the Wii in a heartbeat, because to me a gimmick doesn't outweigh fun video games.
I, and a lot of other people I know, hardly even use the Wiimote as it is. Most of my friends who are Wii owners ALWAYS play with the GC controller if that option is available. I think Wii is doing well because it's a fresh idea that garnered a lot of interest coupled with Nintendo's absurdly good first party game development. It's something different and interesting for people to try. If all 3 systems move to a primarily motion-control setup, though, you will no doubt see tremendous backlash.







