The possibility for that is very difficult to happen even though maybe all countries have recognized that bitcoin is a legal payment tool. because all countries also wish to be the best and get recognition, which will probably become obstacles later. uniting in a legal currency for an entire country might be difficult because of the culture and feel of a decisive country.
I think this is why those countries actually need to leave the idea of them creating their own currency because it will just be unnecessary competition everywhere, they all have one common goal, and that is their responsibility to the human being that has been placed in their hand to control, and having one single currency will only unite majority of these brings in different part of the world together.
This is what many of these big countries like china, Switzerland, south Korea, France and the rest have seen that is making them to now give a thought to cryptocurrency, even though they are still, kind of shaky about it, but I am sure that soon than later, they will all give in to bitcoin usage as one coon currency amongst them all which I don’t think that it will have any negative effect on any of them, except for their selfish nature.