this is part of what nostr:npub1t89vhkp66hz54kga4n635jwqdc977uc2crnuyddx7maznwfrpupqwra5h9 's merkle dags could help with, creating high level, divisible units of the branches of related trees
at this point the outbox model (like nostrudel uses) is the best solution - advertise to the network where to contact you and where you send your messages