Yes, the movement of population to metropolitan areas will be above 80% within 20 years. These are much more effective administrative units than the old nation-states. Nations will survive as historical relics.
Citizenship could be by choice to either geographical entity or virtual state. Authentication is now being done by biometrics. Individual contracts and credentials are moving to blockchain and this is completely decentralized with no governmental agency required. Your identity is under your individual control and you will become your own sovereign authority.
In this form of administration there is no benefit to be “unregistered” just as you pay a steep price for being outside the current credit/identity system. There is no reason to prevent people from choosing to live in remote areas and to hold citizenship in a form of minimalist association. Almost any version of this could be supported based on allocation of assets as trusts to each individual at birth.
That allocation of assets as personal trust accounts provides the Universal Basic Income that gives people this freedom.
These changes are already beginning but it is a large revolutionary change. The existing planetary model is failing and is already so imbalanced that it cannot survive. At this point the change could be achieved slowly but that would work only if there is time. Climate driven change and resulting mass migrations will not allow that time.
We’re already seeing growing instability in the Middle East due to both climate change and fighting over petrochemical assets. That is a result of the economic failure of radical capitalism with unsustainable growth models.