I do not think that will happen. Why ? Because bitcoin can not be related to banks and also bitcoin is very contrary to the bank. And the government also has not legalized bitcoin. If bitcoin becomes the national currency then maybe not one country but all countries.
There is no possibility abiut bitcoin being national currency there are possibility that countries can adapt blockchain technology to have their own crypto currencies like Venezuela is planning to have their own crypto coin named PETRO so we can expect these kind of countries to use bitcoin as the best alternative for currency if bitcoin gains stability.