Then the problem instead becomes what is a valid comment, and a valid commenter (identity). Otherwise the vast majority of comments will be: WaNt A BiGgEr SoMeThInG? Go tO wWw.S0mEgR0$$sItE.cOm
There should be at least basic formatting filter that would block 1 MB comments or clearly non human written comments. This won't stop the spammers, of course. It should be time consuming to create a user id. It should be anonymous, but it should take a few minutes of your time (not your CPU time) to generate a valid user id. once this is done, it'll be easy to spot one spammer's comment, find all others (since comments are signed with ed25519) and dump them all. The spammers then won't be able to delegate the work to scripts.
