Personally, i don't see any reason while other countries will choose to make or use Bitcoin as their sole local currency becasue Bitcoin is decentralized, no one has control over it. Basically, no government will ever think about this becasue they all want powers to oppress the people which Bitcoin won't give to any country that accept it as a currency. Moreover, Bitcoin as a payment method can be use by country alongside the country fiat currency and still stand as a decentralized coin.