How can it be?
Why would any country accept a totally global digital currency as legal tender in their country?
A currency with open source coding and not controlled by anyone,
A currency which can be forked by anyone at any time.
The answer my friend is no.
Why couldn't it be? People don't need a country's permission to use cryptocurrency. If people worldwide accept Bitcoin as a means of value transfer, then it could very well become the world currency. Perhaps even the UN might legalize it even if individual nations see it as a threat.