It'll probably be the smaller countries first where they don't have great currencies to begin with, so they'll always have to use a foreign one, either USD or an alternative. With USD, they are at the mercy of USG and will get pushed around by them. With Bitcoin, the network itself is kept safe with all the energy and mathematical properties, but the price is very volatile at the moment, though volatility will decrease with increasing market caps.
This will be a very interesting experiment to watch.