The reason Nostr is currently monothematic is there are no relay level moderation tools in open source relays. Also few clients allow users to browse by relay. So people cannot force different topics.

We need a relay with easy intuitive moderation features, the ability to assign moderators. Then we need a ansible repo to help others deploy a group of nostr services that work together.

Example, a relay, A ui, a picture hosting app, a database.

A good community implementation will also help but the current community nip needs a lot of work. Because it doesn't really work at all. More of a bulletin board.