Feels like it's what @General Ned Ludd and @npub10td4...x2wl have been doing in their group impls. They just use NIP-44 instead of MLS. IMHO Large Groups do not need the same level of privacy that DMs or smaller groups need. It all depends on the size and expectations. It would be nice to have the group ID derived from a seed so that the group can be split into as many subgroups as necessary. Clients would just derive... say 300 ids... and subscribe to all of them. Similarly, they would also randomly choose an ID out of the 300 to send each new message.