In a smart home it could be used to offer help:
"Would you like some help with that recipe, Dave?"
or it could monitor patients or workers to make sure they are doing what they are told.
The study also reveals that there is probably enough information in how activities are performed to recognize an individual — so providing yet more biometrics.
There are clearly a lot more things that we can teach the Kinect to do with machine learning than just gesture recognition.