I think it’s natural that there should be a small collection of large, production-class instances that host the vast majority of users. The important point is that there are more than a few, and certainly more than one.
I also think it is important for instance admins to lay out their plan for how they intend to host and fund an instance if they intend to be production-class.
We also need some kind of account backup and migration tool so that if an instance goes down, those users can easily recover on another instance.