Of the themed instances that exist now, I’d be willing to bet that in addition to their local communities they host that they also subscribe to other communities that aren’t strictly related to whatever theme they are going with.
For example, I’m sure the Star Trek instance also subscribes to the [email protected] community so the admin can stay abreast of Lemmy news. And probably also follows other technology related communities as well.
I think most people would just want to gravitate to whatever they want to be identified with. There’s nothing stopping you from joining a music themed instance and then adding some non-music subscriptions to your list. It doesn’t force those subs on anyone else on the instance.
And if you don’t want to be identified with any specific topic or community, you can always join a general Lemmy instance like Beehaw or Lemmy.world and subscribe to whatever you like piecemeal.
Community discovery that spans all federated instances should be one of the top things that development should be working on. And it should be integrated into Lemmy, not as a separate website people have to go to and search.
Peoples are lazy. They don’t want to have to go to some separate website and then search for something. And lets not even get started on the difficulties of adding a remote community if your instance doesn’t know it exists, its wonky at best.
If a user cant type “Stephen King community” in the search bar on their instance and then get results, they are either going to assume it doesn’t exist OR they are going to be hitting that “Create Community” button.