Right now we have moodle.org maintaining its old registry database for historical sites. Those then get periodically synced to moodle.net.

I think this is the wrong approach - and think its lead to some duplicates appearing in the database which cause problems. Additionally there is legacy logic going on there (e.g. trying to subscribe people to the old mailing list).

I think that instead we could make the moodle.org just send the data straight to moodle.net at the point of a 1.9 registration and no longer need to keep these two databases in sync.