I invision sort of NIP-clusters, where people within a certain topic area or branch can geek-out together, without involving people who have no invested interests in their work.

You don't need to ask for permission.

Just build.

So, if you develop a Nostr search, browsing or querying tool and you limit it by kind, you will soon be filtering out most of the notes.

Which is fine, if that is your intention, but it means there's now a market for a more kind-agnostic tool.

And that will be the biggest, most-dynamic market.