Just wanted to revive this thread to see if anyone knew anything more in the way of head tracking support in HoS.
I set up my headtracking today, but I didn't use TrackIR. I used a Wiimote, some IR LEDs and a software suite called
FreeTrack. In total the entire project cost me less than AU$20, and now I have a great 6-degrees-of-freedom headtracking system. Setting up a 2-degrees system is much simpler (one IR LED plus one AAA battery), but more limited. Anyway, it shows that even if you don't want to spend $120 on TrackIR, there's a cheap and easy way to get headtracking, so you don't need to be at a disadvantage.
Anyway, I'd love to see freelook in HoS, especially now that there are modelled vehicle interiors. FreeTrack or TrackIR interfacing would be good, as would allowing us to bind freelook directions to keys, or hold-down toggles, or joystick axes. All of them would be fine!