The current workaround for this would be to use an app like IPWebcam and route the network traffic over USB with adb, then ffmpeg it into v4l2loopback on your computer.

I have been using an old smartphone as webcam for quite some time now, and I got to say it works quite well. The only problem is the power supply, because video recording draws a lot of power it drains the battery even when it's plugged in.

Of course, an out of the box solution with UVC would be much nicer!

I tried to use a smartphone (moto g2)as a camera IP. Heat would shut down some components at some points, the camera or the app would crash, the wifi would shut down and not reconnect.

All those problems went away when I switched to pi zero. Other problems invited themselves though.