Moderated content tags/collections. Any user can start their own collection of notes and start tagging other people's notes as being in this collection. They would then be able to set up a user whitelist or blacklist so that other users can tag notes the same way, while the tag owner still has ultimate moderation power over the tag. Additionally, the owner should be able to set other users as trusted moderators of the tag/collection or transfer ownership of the tag or collection.

Clients and relays would then be able to use these content tags in order to create more sophisticated and transparent feeds, searches, and filters. Users could blacklist certain types of content as identified by someone they trust, or they could create their own tag extending and overriding someone else's tag.

Nostr's biggest virtue and challenge is that every note is judged on its own. That means that we need more sophisticated techniques to judge these notes, and we need a decentralized way of introducing specialization and avoiding time wasted from multiple people having to sift through the exact same notes.