Ruled by Physics on Nostr: Yeah but with Nostr some other client will offer a copy of your service for free - ...

Yeah but with Nostr some other client will offer a copy of your service for free - and they will get the users. People will on average go for the cheaper of two alternatives. I am already using three Nostr clients. Will likely try more soon. You can't count on subscriber charity.

If you are talking about corporate services - we are no longer talking about user subscriptions as a way to monetize. Corporate services is something else in my opinion. But by all means, that is also a battle tested way to monetize.