What about redundancy of user data? One of the selling points of nostr is knowing that if a relay goes down, or if a relay operator decides to shut down their relay for good, that my data exists on other relays. I don't think you could convince me that my notes only should be on one relay.
Discussion
you could give it two relays. Basically, you should be able to give your friend an onboarding link to a client, and that client will startup with the relays you gave to your friend. That way, they have a less than zero chance of sticking around. Right?
edit: greater than zero
With gossip, your notes don't just exist on one relay.. But the onboarding relay can have a combination of your notes, notes you've replied to, your friends, etc.. Gossip can still publish to all relays if you want, you can even set it up with blastr. It works.