Other relay ideas (not very good, just to sparkle your imagination):

- a relay only for people with top-level domain names (no "@" at the NIP-05)

- a relay that only stores the most recent post of people

- a relay that only stores posts that have received at least 10 replies from other people (big threads)

- a relay that only serves posts to people "bitcoin" on their profile metadata

The most interesting crazy relay idea to comment on this post will earn a marvelous prize of 10000 sats.