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.