I think it would be a great project.  I would not worry about the full cage, or the multiple wiimotes for turning in circles.  The difficulty I see there would be with coordinating the direction you are facing with the balance board and your center of gravity.  I would also think it would be difficult to turn in a circle on the balance board without it trying to move you around as well.

I think it would be enough to have the 6dof for your head and looking around, and then using a second wiimote for aiming and firing, with a nunchuck connected to it for changing the orientation of the body.  I would see the myvu as your screen.  Attached to the myvu would be the 3 ir leds needed for the 6dof.  By the computer you would have a wiimote to take care of tracking the leds on the myvu.  The player would then be holding a wiimote with nunchuck for aiming, shooting, and the other assorted things needed when playing the game, and the nunchuck for body orientation (direction the body is facing).  The player would stand on the balance board and use it for the actual movement - lean forward to move forward, back to move backward, and to the side to strafe.

Not sure if the myvu would be good glasses though, because I believe the glasses would need to block out more of the world than the myvu - it will also be nice once the glasses can get a better resolution...