I believe in the long run public relays won't exist anymore, they're too easy targets for spammers and sybils and other evil agents. So what relay models could exist?

1. closed relays with manual whitelisting;
2. paid relays;
3. invite-tree relays like wss://pyramid.fiatjaf.com;
4. wot relays;
5. pow relays like wss://labour.fiatjaf.com;
6. <add new ideas here please>