Reply spam can be dealt with by using special subscriptions on the reply feed of each note:

- from any relay: query replies by people you follow only

- from paid relays: anything

- from relays that have antispam mechanism built-in (e.g. powrelay.xyz only has notes with some proof-of-work, nostr.zbd.gg only has notes from registered ZBD users etc): anything

- from any relay: query only notes with id starting with 0000 or something like that

What do you think?