[klem]

One solution to full headtracking could be something like the magnetic flux detection system that was used on some military simulator visuals back in th 80's. It was used to track the pilots eye vector or 'Area of Interest' for projecting high difinition display only where it was needed against a lower resolution 360' background - a remedy to the processing power needed and the limited technology of the day. The magnetic source was carried on the top of the helmet (read headset strap for us) and a detector fixed to the canopy overhead. It could perhaps be done with LEDs similar to TrackIR but allowing much more rotation of the head.

For that to be useful you would need these goggles or perhaps three or more displays because you would not be facing forward when "looking over your shoulder", something TrackIR currently manages to do on one screen.