@f0x mjolnir is using https://github.com/matrix-org/matrix-doc/blob/msc2313/proposals/2313-ban-lists.md and luna uses (atm) a loose variation of https://github.com/matrix-org/matrix-doc/blob/matthew/msc1772/proposals/1772-groups-as-rooms.md (which is older). Mjolnir therefor has an implicit history of bans across a group of rooms which can be applied to new ones, which luna doesn't have. Luna keeps all it's state inside stat events and only uses config for things like account credentials, but this is probably bad since for some reason there are no event filters in the CS spec for the https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-rooms-roomid-state room state endpoint, and this is going to be a shot in the foot for mscs like 2313 in the future (Using the room messages endpoint to filter is not sufficient, as state can be introduced via tombstone and create events).
Mjolnir has an actual matrix dev working on it and will probably become more stable/useful than luna in the near future. If I had the time, I could probably align luna to the new msc in a day or so.
Luna also isn't finished and doesn't have room acls etc.
So yeah Mjolnir will make luna in it's current state obsolete .
Smol server part of the pixie.town infrastructure. Registration is approval-based, and will probably only accept people I know elsewhere or with good motivation.