This is the one place I think it could make sense to use a blockchain for global consensus strictly to help map pubkeys to relays
Discussion
There is no need for chains for this. Each relay can just store their events and sync as needed.
If I have a Pubkey but nothing else, I won’t even know which relays to search. I a world where Nostr has billions of users and there are thousands of relays, having a single space to discover where a Pubkey advertises where they publish notes would be useful