> OpenBSD invests a great deal here. They have their own fork of Xorg (or was that XFree86?) that runs not as root. As far as I know that's unique amongst libre *nixen.
It's a standard feature of Xorg nowadays, but it's only a feature of vanilla Xorg for a few years.
AMD only added KMS to their proprietary driver last year, and Nvidia this year (and IIRC only in a beta driver so far); and systemd makes the permission handling a lot easier. So Ubuntu will transition to it eventually, but didn't have all puzzle pieces until too recently for even 16.04 LTS.
It's a standard feature of Xorg nowadays, but it's only a feature of vanilla Xorg for a few years.