Yep, but you could get exactly the same UX from IPNS + ActivityPub. An IPNS address is a public part of a keypair, and you can publish the assigned content address signed by the private key. So an IPNS-addressed outbox works the same as Nostr. Btw, on Nostr you have to poll the gateways for the content, but IPNS uses one global DHT where you always find the content.