The world doesn't necessarily need it nor want it as each countries have their own working currency. Integrating this kind of decentralised currency in such a large scale will be hard, not to mention, problematic as not all people are inclined in digital currency.
decentralization of the global currency will only give birth to various unfair interests and this is worse than the central monopoly, many people who cannot compete or even become followers will be isolated by greater interests.
But if the currency is separate and is considered a common currency, it will still be considered feasible because after all the currencies of each country still have to remain independent in accordance with their respective regulations.