If one day most of countries in the world ban BTC, will someone with a lot of money spend million or even billion of dollars to establish a whole country. In this country, you will exchange with BTC and other crypto. Will you leave your coutry and move to this 'wonderland'?
i dont think that would ever actually work out, even for a decade. why? unless this hypothetical country can produce literally everything it needs, from resources, technology, services, infrastructure, manufacturing, etc, it will need to trade with other nations. if those countries that the hypothetical country would need to trade with had banned bitcoin, well, they simply couldn't trade without a means to provide something other than bitcoin as their trading tool. sure, countries could provide other goods (essentially, barter) to trade with, but i think the world economy is fairly stable in who provides what. Of course, this could hypothetically be overcome, but it's unlikely without a globally accepted currency to leverage with.
Also, i highly doubt that any one country can be entirely self - sufficient.