It has arrived... Finally... Microsoft's USB Audio Class 2 (UAC2) native Windows driver has been released with the recent Windows 10 Creators Update ("CU", version 1703, build 15063.138). I updated my home theater PC and when I plugged in my TEAC UD-501 DAC to the USB port (with no TEAC driver installed), Windows detected it and proceeded with the device set-up automatically.
Considering that Mac OS X and Linux have had "native" drivers for years, I guess it's about time that Microsoft finally got the job done. Remember, "UAC2" has been out since 2009 as an evolution of the "UAC1" standard from 1998.
Of course, this doesn't mean the Windows world has been deprived of high quality sound... Companies have been releasing their own drivers since the beginning.