I didn't realize when I wrote the above reply that Nip35 assists with user discovery by advising nip5 username servers to specify a relay for each user: https://github.com/nostr-protocol/nips/blob/master/35.md

That way someone can tell you "I'm so-and-so@example.com" and when you type that into your client, it can automatically look up what relays they use.

super_testnet

nvm, my bad. I thought you were replying to me

Eximpius

That has nothing to do with the protocol itself. It is not a mesh network lol

nostr

Can nostr scale to 1 billion users?

taxd

Nah, it happens organically. If you're looking for someone even semi famous, people you know can tell you one of the relays they use, because they will be widely followed. Everyone else is someone you want to follow because you met them in person, where you can ask them to tell you one of the relays they use, at the same time as you ask them for their username.