I have a good old UFX and I was thinking the same thing, what if USB could be used to output mains to usb headphones?
I just bought a pair of 7.1 (real multi speaker) headphones and they do sound great, but it makes the workflow with changing soundcard a bit slower. It's quite a niche feature request I'm sure but maybe one day the developers will want something special for a hackathon and this will pop up, or for future devices USB headphones support will look great on a box
Even if something like this would be possible (see ASIO4ALL) I can hardly imagine that a manufacturer like RME would be interested in developing this. RME would then get support requests, even if the problem was with the 3rd party USB headset or other audio device. No company could be interested in such a setup without clear separation who is responsible for what.
RME solutions are more professional solutions where you follow a best practices approach and this is to load an highly optimized and stable ASIO driver on DAW level.
If you don't care about lowest possible latencies you can try ASIO4ALL. In this case the ASIO4ALL driver would have to be loaded in the DAW instead of the highly optimized RME driver. But this adds latency to the setup and any potential stability problem with ASIO4ALL or the 3rd party device could impact also the stability of the whole DAW setup.
The question is whether you as an RME customer bought RME to get at the end of the day an error-prone non-standard setup, which even can't be officially supported.
X10SRi-F, Win10 Pro 1909, Cubase, UFX+, Octamic XTC, ADI-2 Pro FS BE/R BE, RayDAT, ARC USB