I've only used steamVR headsets myself, but there is OpenHMD which enables at least some functionality on headsets such as the CV1.
The hard part is the 6DOF tracking. Gyros and accelerometers are easy, but constellation or SLAM tracking is another matter entirely, and all the existing code for that stuff is proprietary so it has to re-implemented.
Outputting an image signal, also easy, accounting for the optics on a given set to correct for lens distortion, hard.
I think the CV1 or the PSVR HMDs are the furthest along, and I don't see any WMR HMDs supported I'm afraid.