Firstly, I really don't think governments can come together to agree on one currency. And technology is fast evolving we almost cannot determine how it'll go or what it's future is like.
But I think we can be prepared for whatever is to come.
Government can do it, because since existence of bitcoin government is looking for one or two ways to eradicate bitcoin or bring bitcoin down more especially not to be influential, so with that scenario it's obvious that bitcoin is problem of government because if it's not so, government would have free bitcoin, because right now some countries never legalize adoption of cryptocurrency to their society.