One idea could be a consumer server that takes in all the posts and auto - reposts anything that has more than X likes — but that’s not X ppl can post from this account, I don’t think that exists but I could see it existing in the future
Discussion
Ideally idiomatic nostr, it's times like this more crypto knowledge would be useful. At least it's easy to bandy about terms like Schnorr and accumulator. Communities or like you said a server may be the way to do it as v1. nostr:npub1l2vyh47mk2p0qlsku7hg0vn29faehy9hy34ygaclpn66ukqp3afqutajft says nSecBunker.com could be used.
The idea I'm thinking of is a bespoke community based on place. I post a QR code somewhere and then people can join a community around Trafalgar Square or Central Park and anyone could post in it and your normal moderation tooling (WoT?) or blocks would apply. Like a physical town square. The thing that would be nice however is a revocable secret required to join so only people who'd physically been there and scanned a current QR code could join.