I also wonder how Nostr is useful here. The central idea of Nostr is that it's a lot harder to deplatform people, because a user can publish to several independent relays. Buzz is self-hostable, which removes the risk of deplatforming.
You may want to participate in multiple communities hosted by different people, but with the same identity everywhere. Provably you to anyone that reads your messages.
Initially I didn't see much benefit either, my point was just that there would have to be some interface that the client and server would have to speak, right? So why not Nostr? Why invent a new one? It could not benefit anyone, but also wouldn't hurt.