@mpuckett main thought -- as it is designed right now it seems not too different from Mastodon v4's new feature where you can "follow" a hashtag.

So with that, I post to #/foo, and people can subscribe to it, and anyone who posts to #/foo, that post shows up in the home timeline.

With yours, I mention @/foo, and people can subscribe to it, and anyone who mentions @/foo that post shows in the home timeline.

The difference I guess is with hashtags you don't have to subscribe to participate...