This is looking great!
I recently setup a Discourse server for our CoSocial Co-op that runs a Mastodon server. I ended up setting up OAuth2 plugin so we only accept logins from our Mastodon server → https://members.cosocial.ca (pretty plain new install, just “proof of OAuth”).
My question / feature request is that it be possible to stage/merge Mastodon actors into Discourse accounts, so when accounts on Mastodon reply, they can be linked / owned by the Discourse account associated.
How Lemmy Doesn't Do This
I documented how Lemmy doesn’t do this – you can interact via Mastodon, and an account is created in Lemmy for that Mastodon account, but you can’t actually login and use first class features of Lemmy with your Mastodon account.