here's a brainfart NIP to solve this problem:
introduce PoW scores for notes as a filtering criteria on relays
a note is only published if it carries a hash above some difficulty
higher difficulty notes are less likely to be published
Discussion
oops sorry, correction:
higher difficulty notes are more* likely to be published
whenever there's spam, relay will raise the difficulty threshold
ok that's exactly what [NIP-13](https://github.com/nostr-protocol/nips/blob/master/13.md) does
Allow me to introduce another PoW enjoyer.