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.
It is possible if the central bank finds a way they can still control the crypto currency.
Central banks only care about if they can control the currency they issue, they don't care too much whether it is crypto or not.
That is not the issue, the issue is if you think that a IMF crypto is going to be accepted by the likes of Russia and China? What if they dont accept, what is going to do the rest of the world to make them accept, not much since those countries have nuclear capabilities and god knows what other weapon they may have.