Thibault Martin commented:
Both Bart, Andrea and Emmanuele expressed concerns about anyone being able to create a :gnome.org Matrix ID. I’m guessing the threat model is that somebody could impersonate GNOME Foundation members.
Their recommendation would be to keep the :gnome.org strictly for GNOME Foundation members, with LDAP authentication. Nobody else could sign in and create an account or a room on :gnome.org homeserver.
If we wanted to follow the direction of making Matrix the recommended platform for projects related to GNOME (be it a Core component, or a new GNOME-friendly app that would later check all the boxes to join the Circle), it would make sense to have the Matrix rooms of these projects hosted on the :gnome.org instance. It would make it impossible for non Foundation members to create rooms on the homeserver, which would limit a lot its adoption.
Alternatively, since applications are migrated manually to the World/ or GNOME/ group, it could make sense to create the room on the homeserver at that moment if the maintainer asks one, and grant them Moderator access on the Matrix ID of their choice.