Hi @flfl, yes you are correct that our own library does converse with that of HTC to provide the XR SDK so the low-level layer is ‘opaque’ yes.
For the time being, we are focusing on the Windows platform under VR which provides that grand majority of software currently available, so Linux support is unlikely to be prioritised in the near future.
Accordingly, it may be worth your time to petition HTC directly on this point.
With regard to the Tobii Pro HTC Vive VR, this was sold via the Tobii Pro Business Department, so please directly queries regarding this hardware to their dedicated team @ https://www.tobiipro.com/contact/sales/