A fast paced FPS would certainly be more challenging to design, but I am sure there might be a way. Microsoft has purposefully crippled the accuracy of the Kinect somewhat for some reason, so enabling the full resolution and with future developments I am sure it will become a reality pretty soon. To change weapons might require a hand gesture to the side or drawing a shape in mid air. Ducking for cover might require you to kneel down and the orientation of your arms might tell it what direction you want to to take cover too. This would be with a FPS with shooting areas similar to 3rd person shooters like Mass Effect where you advance past distinct cover objects. More open plan games like CoD would be very much more difficult I imagine.How would you implement this in a fast-paced first person shooter?
What action would you perform to change weapons, fire or reload.
Evasive action?
But that is for shooter games. I am sure you will not have a hard time finding people that would murder their families for an opportunity to play WOW in VR.
Once the price drops substantially. 
