My system is built with -elogind set globally and is thus, free of elogind. I use lightdm as display manager and mate desktop environment.
To my surprise, when now starting xdm, it fails saying it requires elogind, for some reason, even though it never did before, preventing me from starting the graphical environment.
Modifying line 57 of /etc/init.d/xdm to remove elogind allows me to start the xdm service again.

As I understand, this dependency was added because gnome outright requires elogind. I don't want to accidentally start bikeshedding, but maybe adding a elogind USE-flag to the xorg-server ebuild to toggle the requirement check, with gnome asking for that flag there as a dependency could solve this?