Just drafted a couple new nips for private groups (rebranded as "closed communities"). I'd love your thoughts:

https://github.com/nostr-protocol/nips/pull/875

The goal is to introduce as few new concepts as possible, instead composing existing functionality together (kind 30000 for member lists, and building on nip 72 communities). The benefit of this is that we now get hybrid communities, which can be partially public and partially private, which could have some interesting use cases.