I'm not only thinking about political bubbles here, but linguistic or cultural ones. For example, when I joined a server here, it was federated only with a few other small Japanese servers, resulting in a fairly miserable experience. Another set had multiple languages but was just devoted to art. It's incredibly difficult (or was a year ago) to find servers that are general purpose and federated with both Japanese and English servers.

It's actually kind of interesting that me mentioning bubbles resulted in an immediately political assumption; I guess it shows how out of touch I am with mainstream Twitter.