Ross, once you understand nostr better you will find that "the protocol" is not even well defined. It's a loose collection of NIPs (on which we mostly agree, especially NIP-01).
There is at least one NIP addressing your concern, see https://nostr-nips.com/nip-11#pay-to-relay
A business model for nodes already emerged spontaneously anyway, one of those is products subsidizing free relays.
We should let free markets will do their thing.