I feel Bitcoin won't be only a currency for a country. Because governments don't want to lose the control from their native currency. Bitcoin is uncomfortable; cryptocurrency means no one would have control over that. On the other hand, transaction fees are another prevention. We know a large number of the population don't know about Bitcoin and how it does work. Those who are illiterate can't handle Bitcoin anyway. So we must have physical notes for our daily life. Which isn't possible; we can't imagine what will happen if Bitcoin becomes a currency for a country.
That’s probably the reason why bitcoin until now has not become a country’s currency, except for El Salvador who made it as an official currency. It requires a mass awareness and adoption, and most likely mass education so that all the citizens living in a country will be informed on how to use bitcoin properly. However, if a single country really aims to use bitcoin in their country, it’s actually possible but it takes a lot of preparation prior to that so that the people won’t get confused and stay complaining in the long run.
The only reason by most governments are beginning consider Bitcoin is due to it's ability to be used as a hedge against inflation, many countries back their fiat currency with Gold, so since Bitcoin is referred to as digital Gold, governments are now buying the idea of wanting to own it, else I don't think any government would've even embraced it if it didn't have such value and only seen as another form of money, cause they still want to be in control and Bitcoin won't give them the opportunity.
El Salvador took a bold step, their citizens should be happy concerning a government that sees a better future with the help of Bitcoin, their government a step that would gradually open the eyes of others to the potential of Bitcoin when it comes to strengthening a nation's economy and against inflation.