Well I think I've solved the conundrum with FPS. Try to stay with me here. This is going to be pretty involved.

One we have to solve the problem of actually shooting the gun. If Kinect has the ability to distinguish between an open hand a closed fist then this problem is solved. Try to imagine your outstretched arm, elbow bent like you are shooting an imaginary gun, except your hand is open instead of a finger representation of a gun. When you want to shoot you just make a fist.

Two how do you solve the problem of reloading? Simple you take your other hand while one is outstretched in the shooting position and hit the bottom of your fist, like you would be putting a clip into it. Kinect will recognize the two hands coming together and reload your gun.Kind of like a motion of paper, rock scissors and you select rock instead  your bottom hand comes to the rock instead of the rock hitting your hand.

Three how do you solve the problem of switching weapons? Pretty simple as well. This is just one scheme idea. Grenades would be on your left shoulder, clavicle area. Touch that area with your shooting hand and it will switch to a grenade in your hand. Then from there throw your grenade in a normal throwing motion. Next for alternate weapons touch the outside of either thigh, right side for handgun (secondary weapon), and left side for primary weapons, or vice versa depending if you're left handed or right handed.

Fourth the hardest solution to come up with is movement. In order to walk forward you move your right foot forward, or left for left handed people. As long as your foot is forward your character moves forward. Move your foot to the left in front of you, you walk left. Move your foot to the right in front of you, your character walks right. Move your foot straight, you get the point.

Lastly crouching is pretty self explanatory, you just crouch. Slight movements looking to the left and right is easily done by turning your torso in that direction.

This may be hard to all take in and imagine but I think it actually solves the controller free problem. Maybe Firebird studios is working on this right now and my imagination will come to fruition next E3. I wouldn't be surprised to see a new graphically superior, full body control FPS coming out for Kinectic created by the newly formed Firebird studios.