Oh, that's essentially what you said 🤦

GitHub

Add nip for key sharing · nostr-protocol/nips@a9f7058

Nostr Implementation Possibilities. Contribute to nostr-protocol/nips development by creating an account on GitHub.

I guess this isn't nip-86 yet but it looks like it would work for paywalled content. people without the shared key would see encrypted data or nothing at all... better would be to make it so they could see how to decrypt it

Haha that was actually drafted by yours truly. So you know my game plan already.

Oh, maybe you already knew that. Sorry, memory like a goldfish. You could indeed use shared keys independent of closed groups