If one country accepts bitcoin as a legal tender it would be halfway to becoming currency. But I do not believe it will happen. As to the reason, same as Visa or MasterCard would not have either word bitcoin or it's logo on a card. It's a branding issue. Card schemes do not understand who or what is behind bitcoin so for them to put their cherished brand next to something they have no idea about is impossible. I would say it's the same with countries.  Most likely they will develop their own digital currencies. I know Bank of England has 3 man team looking into this and I'm sure others do the same. However, bitcoin can be seen as settlement mechanism between other government backed digital currencies. Time will show. But I'm having difficulty accepting bitcoin as a vanila currency in conventional terms.