You're right of course that's what relays do.

And as a user, I'm going to select to use certain relays based on some reason. I am forced to be selective, as there is no global state.

And as I'm selecting, on what basis am I selecting?

I'm selecting on the basis of where my people will see and post notes. I need a word for this concept, so let's say "community".

Yes I'm probably wrong, and meanwhile I'm also building stuff that works this way, and it works well.