I think the thing is, if the admin of your instance de-federates with another instance, you don't have much in the way of options if you want to follow someone on that instance. Or, if, due to bad luck, you originally sign up with an instance that becomes the 8chan of instances, you don't really have much in the way of options if you don't want to be there. You can't take your account elsewhere. You're pretty much limited to creating a new account on a new instance, and then you have to communicate to all your followers that you've moved.