Being that Holiday 2011 will be the sixth anniversary of the XBox 360, I would put the odds of a Q4 2011 release of the XBox 360 at 50%, the odds Microsoft will release a new console before the end of 2012 at 90%, and Microsoft will certainly have released a new XBox before the end of 2013.
Starting Q4 2011, because they have been on the market for a full 5 years, the negative backlash for Nintendo or Sony to release a new console becomes minimal; and, as much as people will claim the first mover advantage "doesn't exist", the XBox 360's sales performance (relative to the original XBox) can be attributed in part to being out before the competition. There is a significant risk (for Microsoft) of allowing Sony or Nintendo to release their systems early because there is a significant chance that either company could produce the "must have" system, and there is very little chance of growing their userbase if they release a console 12 to 18 months after the dominant console has been released.
