Yes this, and I could totally see the startrek instance growing into a hub for sci-fi related communities for example. More important than whether we are spread out is that the possibility and capability we have to spread out or migrate instances keeps instances in check by ensuring they don't have leverage or lock-in over the communities. Currently I think the main risk is communities living on 1 instance, but better instance migration tools would mostly mitigate that - imagine if you could migrate a community (which in underlying activitypub terms is very similar to a user account) to a different instance, the same way mastodon accounts can migrate between instances and keep followers.