If governments ever went with a crypto, they would first make damn sure it's under their full control and regulation or else they're no longer governing anything.
And how do you expect governments of the world to reach an agreements to launch a fully international crypto?
They might have each their own national crypto just as well, with all sorts of country-specific regulations and variations.
You cannot create a national crypto. the internet is borderless. If you are talking about a centralised national crypto, well there is nothing special about that idea.