[antimatter15]

Some more advanced autostereoscopic displays use head tracking as well to configure the paths of light instead of arbitrary prescribed fixed sweet spots. It's also pretty cool in that you could use it to give a different full sized image to different people watching it. So for playing games, you don't have split screen, but rather each player sees their content full size sans glasses. Maybe you could use the ultrasound interference patterns to create directional sound too.