I think the ability to provide angular tilt to the thrust vectors in QGroundControl Vehicle Configuration UI would be helpful (instead of manually specifying all unit vector components – increased error potential), given that it is very common and beneficial to tilt rotors a small angle.
Sounds more like a PX4 feature request to me. Are you willing to dive into the ControlAllocator and make a contribution?
Oh, I was thinking this would merely be a UI change, and that arbitrary thrust vector directions are already handled?