Just as the old churches, once so central to daily human experience that it was impossible to imagine life without them (if one even thought to try), so the centralized nation-state will eventually lose its relevance. This is for some reasons, one being the weakening of the connection between ‘nation’ and ‘state’, once the main driver of state centralization; the ever-falling ROI the state provides for it’s productive and law-abiding sectors, together with state tolerance for non-productive and even destructive behavior by ever growing swathes of the populace; and the rise of plausible alternative structures, much as republicanism in the 1700s was conceived as an alternative to the dominant monarchies of the day.
What will it be replaced with?
One possibility is that various functions will slowly be duplicated by other actors, till these become the go-to address for solutions to real world problems.
So what remains to the state? At the end, all that is really core is, as per Weber, the monopoly on physical force. But even this, like the churches’ monopoly on spiritual belief, can lose relevance if physical force becomes somehow irrelevant, or impossible to apply, or counterbalanced by external forces.