Let's extrapolate, and say that no country should adopt a purely digital currency. Would that be accurate? I don't know too much about the topic domain, so for those who do, what would be required of a purely digital currency to be a good candidate for a national currency?
For a fiat currency to work, there must be faith in the currency and the governing bodies that support it. The US dollar used to be tied to the price of gold and silver, then later entirely to gold, then it was turned fiat in the Nixon years.[1]
BitCoin, in particular, does not allow a central bank to "print" currency (which is a tool used to control the inflation rate). Without the ability for a central bank to regulate the creation of a fiat currency, there would eventually be an erosion of faith in the currency. Alternatively, a digital currency could be tied to a gold silver / other commodity standard, but then it's not much different than any other commodity.
The Canadian bank is experimenting with a digital currency, but it won't replace the paper+coin currency, only augment it.[2]
[1] https://en.wikipedia.org/wiki/Nixon_Shock [2] http://business.financialpost.com/2013/09/19/canadian-mint-p...