That's the massive problem with decentralized "currencies". Even if the Colombian peso is used by 0.6% of people in the world, it's still a currency because lots of people can pay with it in almost all their interactions with the economy. If a decentralized global "currency" is used by 0.6% of people, it's not a currency because almost nobody around you accepts it. Even at 6% it would not be a currency. Maybe at 60%, but how do you get there from 0.6% in the first place?
