By "X-variables" you mean $XDG_CONFIG_DIRS, $XDG_DATA_DIRS etc.? They aren't related to the X server. The "XDG" is for the old name of the Freedesktop.org project (X Desktop Group) [1]. Freedesktop.org is the host for the XDG Base Directory Specification [2]. Apart from that they are also involved in Wayland. So I see no reason for worry.

[1] https://en.wikipedia.org/wiki/Freedesktop.org

[2] https://specifications.freedesktop.org/basedir-spec/basedir-...