The link has a pretty lengthy description of a similar idea for an XMPP server, but tl;dr: it could be nice to have the option to run a Lemmy instance that is invite only and invitations propagate in chains, meaning you remain “responsible” for the people you invite.

This is different from an account approval scheme, where the admin of an instance has to approve accounts, which isn’t really scalable.

I think this could be a nice middle ground between large public instances and small private ones.