I doubt Kinect and FPS are high on MS priority list right now. The focus for Kinect is clearly new owners/demographics and even augmentation of other titles seems to be very low on their list of things to do as well.
Kinect should be able to support a form of FPS, but on it's own (i.e. without a controller of any kind) it'll clearly never surpass a gamepad for that kind of game.
Assuming all goes well with the launch and initial sales I'd expect sometime in the first half of 2011 we might see some augmentation of titles going on.
But, I don't think MS are going to try and support existing owners (at least initially) in the same way Sony has decided to with Move. Which isn't a knock on their approach, just noting MS is going full out for new titles/demographics at this point from what I can see.
Try to be reasonable... its easier than you think...
