Specific musician ones. At the moment there's a bunch of Jeff Rosenstock teases happening and right now is when I'd be going to that subreddit to see others discussing them. But it's gone and at the moment there's no replacement.
I also miss the specific opening weekend discussions on r/movies. I think there is a movies community somewhere but I've not seen it pop up on my "active" feed.
You could always make a post on the general music communities and see if other folks want to chat in the comments? I think we just need to embrace making posts about specific things in communities that feel “not specific enough” but that have enough subscribers that at least one or two care about that subtopic of the larger whole.