I don't think the Xbox could handle it.
For one, you're going to spring an attachment on people, this isn't going to be something out of the box that all Xboxes are going to have. So you're basically expecting someone who wants something with the simplicity of the Wii to pick up a more expensive console, an expensive add-on, and a smaller pool of games? Yeah, no thanks.
Now, if we're talking about next generation, perhaps if this is in the box then you might have a different story... However...
1) Nintendo will still have a generation's head start on working with motion technology, they'll have a headstart in making good motion control games for their next system. Sony might have some too, if they ever figure out what their Sixaxis is actually for.
2) Not all games are going to work well for motion control. We're already seeing some of that in the Wii. And while the Wiimote's stylus pointer system might work for games we haven't seen much good representation of just yet. (We're bound to see more sports and shooters.), I'm not sure how well a camera system would work.
3) People already cry about 'being tired' using the Wiimote. (Here's a hint, move your fat ass every once in awhile.), having to move your entire body to play games, while a cool concept for some games, would a lot of people want to play a soccer game where they had to run in place and kick at the air for over an hour a game?







