With X.Org Server 1.16 officially landing now for Arch Linux, X now runs without root privileges in combination with systemd-logind, but there's some stipulations such as right now launching X through a log-in manager will not lead to a rootless X environment, etc.
With X.Org Server 1.16 also comes the much-improved, in-server GLAMOR acceleration code so Arch's glamor-egl package has been deprecated. New to Arch is also a xorg-server-xwayland package for running X11 applications inside a Wayland session through X.Org Server's 1.16 built-in XWayland support with GLAMOR acceleration.
Lastly, Arch has decided to temporarily disable DRI3 support with their xf86-video-intel DDX driver package because of multiple rendering bugs with the Intel DRI3 support. I talked about the open DRI3 issues recently with Users Warned About Possible Regressions With DRI3.
You can learn more about these recent Arch Linux updates related to the X.Org Server 1.16 upgrade via the news announcement at ArchLinux.org.