The advantages of it is that, it could be faster than to transact than the banking system today and i know there is new regulations that will going to implement to us in the system before we can use the crypto currency freely in the future.
But this kind of thought is too futuristic to happen soon in our life and maybe it will happen after 20-50 years from now. I don't know what kind of technology could someone has to create during that time but i'm pretty sure it's an amazing technology.
Not all countries want transparency and a finite supply of their currency. Just look at how many countries have corrupt governments just want to fill their own pockets...a decentralised ledger does not make that easier.
Therefore it is unlikely we see all countries evolve, but I also think it's realistic to see at least a majority of countries adopt and replace fiat with crypto in the next decades...a possible next financial crisis might be a catalyst to speed the process up.
These two giant countries in the scene of technology will make a great new discovery in the future but it's just too far to happen yet.