For users who don't own a Tobii EyeTracker but have some head tracking system, it could be very useful to have TrackIR/OpenTrack support.
The Tobii support in TheHunter is quite a complex system, but for head tracking I believe a simpler system could be used: just control a 'camera offset'. The mouse/controller would behave in the same way, but you would be able to 'offset' the camera angle to the sides while still walking forwards, but then resetting the offset (or temporarily disabling it in aim mode) for example. The hiding of the hunting HUD and dynamic exposure wouldn't be needed, which should simplify implementation.
I think it would be quite useful, hope others do too!