I've been thinking about this ever since reading Snow Crash. But then how would your character walk if both hands are occupied by holding a gun? Some sort of 360-degree treadmill? And then how would the game provide physical feedback (say, your character runs into a wall)?
A grid of trackballs that you walk on, essentially, with slightly higher rolling resistance so there's some ground friction. The "wall problem" is mostly intractable, barring utility fog.
you could simply put the controls on the gun like in the Cabelas dangerous hunts game. They managed to cram an entire Xbox 360 controller on to their gun periphial. I've longed to use this with other games and the kinect.
