This is tough. I think its selling point right now is the dance game but that will get old for a $400 (console, kinect, and game) buy in. It it were to be dropped in price OR another big push game launches then it could do very well next holiday.
I think that is possible so, I'd go with 20m by 2012.
You got 10m in first 4 months (nov-feb). About 4m is a good sell through for next 7 months(mar-sep). Then another 6m in last 3 months(oct-dec).
Seems reasonable.