I think it is very unlikely that we will see a worldwide crypto currency issued by a central bank since that will require a government so powerful that it can impose his will above the will of the other countries and while the U.S is very powerful is not that powerful.
Never say never. There was no single country which was very powerful in the Euro zone. Yet, we did see the Euro replace the lira, drachma and the deutsche mark.
The euro was made possible by the power and size of the France-Germany axis. France was able to get Germany to agree to the euro by agreeing to German reunification. If power was more dispersed across Europe, I'm not so sure if the euro would have been born.
As I mentioned, modern money is a political as much as an economic product. And politics is not looking good for the dollar-based system (or any future IMF-based system which is really the same thing in a different guise) after this US election!