One only need to re-implement the interfaces actually used by the DEs. IIRC GNOME had a page listing those interfaces on their wiki and systemd has remarkably g

One only need to re-implement the interfaces actually used by the DEs. IIRC GNOME had a page listing those interfaces on their wiki and systemd has remarkably good documentation about its public interfaces. Also consider that until now many of the things you listed were done by shell scripts that every distro reimplemented differently, so if you're happy with such ugliness you can pick it up as-is. ;)