It seems very hard for Krypton to take the place of money for real. This can take many years to become. And that time is also very variable. Crypto can be a common currency. But the whole world needs to accept it.
Absolutely this is not possible in near future. Crypto might not be able to replace fiat as long as all the people around the world have access to technology and are able to use crypto as alternative to fiat. Besides, countries tend to have a unique profile from others and this is the reason why fiat will still survive even if Bitcoin starts ruling.
Bitcoin can be used as international currency but it will never be the national currency of a particular country and every country around the world quest for their national identity as well.