Built an initial prototype of showing the desktop window screencapture inside VR (while in Freebird), using the mss library. Freebird will have to install it using subprocess.run([sys.executable, '-m', 'pip', 'install', 'mss']).
It works, but is currently a bit laggy. The capture and processing happens on a thread, and a timer modal calls the actual GPU texture assignment. The GPU texture assignment takes about 2 ms, but the XR view is still juddering (way more than it would with an extra 2ms of latency). Still need to investigate and smoothen the performance.
But it seems to work well overall. I even drew a tiny placeholder cursor, and it casts the entire screen, so it's possible to switch to other programs while in VR in Freebird. Promising.