Seems unnecessary to do more work when the work has already been done and can be verified?
nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s, could I try and bring https://github.com/damus-io/damus/pull/172/ up to date (probably as a new pull request) so that Damus sends messages with PoW automatically? I know you said that you think Lightning is a better filter, but every single person sending notes on Nostr can calculate PoW since they obviously already have a computer whereas the same is not true for Lightning. If Damus leads the charge on this and if we can get nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z on board we could make PoW default on notes which could almost completely solve the spam problem.
Discussion
The verification signature only proves that the note was signed by the senders pubkey and that all of the information is correct and untampered with. PoW means expending CPU power (like I'm doing for this note) to create an signature. This would be possible but expensive for spammers to accomplish.