In coming future, we will have a situation when you must use internet or have internet or you will not have anything or use anything so internet will be everywhere everywhere where people live so it can be internet based and must be i say.
As time and technology develops, everything will be based on the internet and to fulfill it all, maybe that's the reason why crypto currencies are created to keep up with the times and technology with the economy
As for now, we can consider Bitcoin as our only global currency so far because there are lots of factors that a global currency will not going to happen. If the world wants a global currency i think it's Bitcoin since no one is controlling on it but the problem is that it is not stable and is subject to high price volatility. I don't think any country would accept that if there are whales lurking everywhere.