Yeah, topical relays that are moderated by the relay owner and moderators. nostr:npub10npj3gydmv40m70ehemmal6vsdyfl7tewgvz043g54p0x23y0s8qzztl5h sorta had this going on with relay.tools

The algo is basically hashtags, event kinds, the relay owner and moderators curation.

Really only works with paid realys or spam and off topic posts overtake the relay feed.