I guess "difficult" is the better expression. Dont underestimate the power of the rulers. Its not a question of "can they do it", rather a thing of "how many laws, personal rights, constitution clauses ect. are they prepared to ignore".
This is a battle for world currency domination, so you can assume that those who are in power now will do just about anything to keep the status quo.
It will be interesting to watch where all this is going.
I think if Libra can be established as a stabile international currency, this will be the Kryptonite for the central banks and the state issued currencies in the world. Of course the same can be said if corporations like Alphabet or Amazon issue similar currencies.