At first when I read the title I thought "what's the point in integrating Kinect with WP?" but on reflection I think there is one possible way of benefitting. The Kinect naturally picks up your skeleton well, but the advantage of the WP device is that it has sensors, e.g. accelerometer. To me the video posted doesn't technically integrate the two. The two devices are acting largely independently.

One possible case would be if you could think of a benefit of having Kinect + a camera looking back the other way. Afterall, a Kinect can't normally see backwards.