This is very cool! One question would be - since this is a normal nostr event, it can get easily reposted and it would become free. The reason it got reposted does not have to be malicious. Quoted and included, someone clicked rebroadcast. Even with paid email list, anyone could of course forward the paid email, but this is different because it can happen in many ways which are not obvious to the user or the author. I don't have a better solution, or a better way to handle this, just pointing it out, maybe someone has better ideas. Can't wait to try it out.