It is impossible for bitcoin to become a national currency from a lot of reason. First of all the transaction fees are t high and also the time that it takes for a transaction to be confirmed is pretty big if you pay a small fee. If you want to buy a coffe or a juice you would have to pay 5-6$ for the product + 4-5$ the fee for transaction so at the end you pay double the price.
The second problem is the big fluctuations of the price. One day a bitcoin can worth 8000$ then the next day it worths 6000$. This will obviously affect a lot of merchants because most of them have to calculate their profits everyday or every 2-3 days.