/u/porn was active here briefly, make a load of communitiess like /c/Boobs and has since not been on, leaving those communities unmoderated. I’ve messaged them about being added to some of them (like they offered), but no reply.
I think the larger communities, at least, should have more than one moderator to cover different timezones, being unavailable or disappearing. I assume that admins can add moderators to comms, right?
I think for this you really need to rope in the admins to create a system for installing moderators to unmoderated communities. That, however, can only happen once there are enough active mods on the site to begin with, which will take time.