Some apps, line mine nostr:npub1pu3vqm4vzqpxsnhuc684dp2qaq6z69sf65yte4p39spcucv5lzmqswtfch do support choosing which relays to publish to.

I think we could have relays that only host a part of a users posts, say those in a community / group / connected to a list / or with hashtags.

Also we’re building a viewer which shows who’s using and what content is on a relay. Hence I wanted to see what topical relays / content focused ones exist to test it out.