I like this idea. However, following someone now is simply a matter of adding a pubkey to a list. A client could add it, but someone could simply use another client to follow for free. Seems like it would need to be added on the protocol level. Maybe call it a “subscribe” and require that the one being subscribed add the pubkey of the subscriber to a “subscribers” list. Then pay relays to only send messages to those in the subscriber list?