Just wanna add to this convo that we've been working with interaction policies in GoToSocial for a while now, and the protocol extension described here is extensible to include a canQuote property on an interaction policy: https://docs.gotosocial.org/en/latest/federation/interaction_policy/

Reply, Like, and Announce controls and approvals etc are already running in GoToSocial since v0.17.0 last year. It would be pretty neato if Mastodon could reuse the interaction policy properties and approval flow for quote posts, insofar as that's possible. Have discussed this in the Mastodon discord with Claire as well, but just putting it here too.