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 

 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 

 nostr:nprofile1qqsw3mfhnrr0l6ll5zzsrtpeufckv2lazc8k3ru5c3wkjtv8vlwngkspz9mhxue69uhkummnw3ezuamfdejj7gsdnpq
Allow me to introduce another PoW enjoyer.