Why not?
In some countries like Switzerland it will be very easy.
People there have right to ask referendum about anything they want to change in their country, even national currency.
If enough signatures collected, government is obliged to call a referendum and accept the decision of the people.
So, if we can inspire people there or find enough Bitcoin lovers in Switzerland, we can help that bitcoin become official currency there
In some countries, of course, it will be very difficult to introduce BTC and be accepted, but in some country it will be more easy.
All will depend on public pressure.