I’ve got Evan Prodromou blocked so I didn’t see https://tags.pub when it was announced. If you missed it too: it’s a service that listens on relays for hashtags, and boosts posts containing them, to followers following any given hashtag. To give hashtags much more reachability despite the horizon of federation.

I proposed something like this in the context of natural disaster response. Users could come to a consensus on what hashtag to use for, say, # HurricaneFoobar, and posts containing the hashtag could spread far and wide. But because I care about safety, I suggested that it needed selective outbound relaying, so that only posts containing a list of opted-in hashtags were sent to the relay. I see that managing what gets sent to relays is out of scope for tags.pub.

I also don’t see any mention on the github issue list about tags.pub being able to defederate known bad actors, so I guess there’s nothing stopping your posts from reaching poast and friends, due to ActivityPub’s nontransitive defederation behaviour.

User-to-user and user-to-instance blocks will similarly get laundered, so if you let tags.pub boost your posts you may find unwelcome people reading your posts.

So, this is a cool idea, it could be helpful, but it’s not ready yet IMO.