@Revertron Yes, but this still requires a single database, right? Only the second tier (namespaces) is logically decentralized.
What if there is a single peer to peer network, but multiple databases, each database is completely independent and can not be removed from the network. Like torrents, but with mutability. Is it possible?
In such network clients will only download data they actually need, and each database will have its own rules (small invite-only namespaces, big commercial ones, and everything in between)