Maybe food for thought: One thing that Mastodon has going over Nostr, is branding. I mean, unless you want to "dive" into the third party ecosystem, Mastodon looks pretty much the same, wherever you access it - it's always the Mastodon web client - that's how you can recognize it easily.

On Nostr, many clients feel like seperate entities. Someone may be on Primal, another Iris, another Damus - Seems like these are seperate entities.

When you ask, are you on Mastodon?

It's a clear, yes or no.

Are you on Damus?

What is Damus even?

Oh, it's Nostr. Is this, like the internet?

I still think there's no good solution here; I wonder what's more mental overhead for users: Mastodon with multiple servers, or Nostr, with keys and relays.