The NIPS 13 is already marked 'optional', so even the original idea wasn't forced. I am not even suggesting that, exactly.

I feel like 'Paid Only' Relays create a Nostr country club experience, keeping real people out just as well as spam. They're not a solution to spam that is acceptable, in my opinion, dividing the community and putting up a wall for new users. The alternative is to require the relay operators do this continuous effort to block spam or throw mountains of resources at the relay, making it a full time job to keep a public relay running. Like the blocksize, this determines how decentralized this system can be in reality.

I'd like to combat spam without requiring a relay or client admin to make decisions about what is spam on my behalf. Public Open relays can't accomplish that, they have to make some spam moderation decisions, but public relays that require work or payment may be able to do that, and still be open to all (legitimate normal people, who do some work to prove it or who pay).