> users want a relationship with ONE hosting provider

That's a valid starting point. 
Nostr ultimately incentivizes users to have **their own** relay (+ blossom server) too. It's the most cost effective way to solve for privacy, speed, bandwidth, limiting read-access to publications, etc... 
Plus, in the case where relays are a keypair, it's probably the simplest way to handle key delegation, rotation, etc... too.