I thought Letr was a new protocol, but it's just Substack on top of Nostr. I don't think it's gonna make that much difference unless they make really fast and efficient apps.

I suspect Substack fakes the subscriptuon revenue numbers similar to OnlyFans. Bitcoiners are a very greedy bunch so I doubt they'll donate for just some text. I can see how AI cartoon porn may be in demand though.