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.
I think cryptocurrency will not be able to master the major currencies in the future, as long as the government has a fiat then it will be difficult for cryptocurrency to be the main currency in the future
Bitcoin enthusiasts don't want to make Bitcoin the major currency, they just want to make it accepted and regulated currency, in some countries people use USD more than the main currency of the country, and Bitcoin will occupy the same position if governments regulated it.
Mankind has always used the money to carry out their trade. Therefore, people can not live without money. But we need to expand its capabilities and to start using Bitcoin. The main thing that the government has approved it