Just checked it, thanks for pointing to it. I think it's more of a decentralized encrypted messaging platform, and my idea was to have a way constrain the visibility of the conversations to naturally connected groups of people while giving a way to slowly expand the connections rather then fighting censorship
More or less like in real life, where you chat a lot with your friends, but necessarily with some of their friends you don't know that well. In this case you would ask your friends for the introduction and that what I've tried to model.
One other feature I've been thinking about was to make the moderation automatic in a sense of making signups possible only via invitation and putting some weight on it. Basically if you invite somebody who's misbehaving on the platform and they get flagged, you get penalized as well unless you do it first. My theory is that it should make users care about their digital surroundings.
By default all texts are open. There is encrypted messaging, albeit only used for private messages inside a group or to another person.
What you mention could be achieved with the a nostr relay. Just permit inside who you want, but anyone can keep participating on internet at large with exactly the same account.
But if you want to moderate everything inside, then likely mastodon or a traditional web forum might be more suited.
It permits both private/niche communities and public (global) texts.