This would also solve spam. How cool would it vmbe if marketing and engineering actually converged?
This post made think that for those whose goal it is to #growNostr, which is a lot of us on the network, an invite-only system seems to attract interest in new things. It creates like an artificial scarcity and FOMO. It appears this worked well for BlueSky, and I think even Facebook and Gmail accounts did that in the beginning. Since Nostr is already out there, perhaps a new Nostr client, maybe like the one nostr:nprofile1qqsgydql3q4ka27d9wnlrmus4tvkrnc8ftc4h8h5fgyln54gl0a7dgspzemhxue69uhhyetvv9ujuurjd9kkzmpwdejhgqg5waehxw309aex2mrp0yhxgctdw4eju6t0qy2hwumn8ghj7un9d3shjtnddaehgu3wwp6kyfehcpn has teased, might use that strategy and attract a lot of new users with it. Perhaps you could only login to the client or use it if some existing user has invited you (if that is technically possible with Nostr, given interoperability and all). Then you have the start of a web of trust going in and at least one other user to follow. Just a thought.
Discussion
A NIP-32 label with a PoW invite, attached to the user kind:0?
I was thinking some kind of invite link with a secret in it that would allow the issuer to auto follow the new user. Kind of a referral link. The new user would publish some kind of message only the issuer could read, and the issuer could listen for that and follow on validation. You might want to make these single use to prevent them being stolen and re-used.