That surprises me. I knew there was a hid-steam, but I didn't know its provenance.

FWIW, it appears Valve is sponsoring development now. Vicki, one of the maintainers of the SteamOS kernel, is the most recent contributor to https://github.com/torvalds/linux/blob/master/drivers/hid/hi...

It's too annoying to search more recent linux-input submissions to see if anything has been pushed upstream yet specific to the new controller.