In my opinion, future BTC may be the national currency. Currently it is the world discussed section. It's fast moving forward .
You used a better world for this here, may be. There are people who want to kill other persons in discussion because of not accepting the fact that bitcoins can be dead or they may be devalued after sometime. You are sensible enough to tackle this situation and people are here for making this argument. Yes of course bitcoins can be national currency but it will be shown by the time.
I do not think so, first of all, Bitcoin limited at 21 million coins for its supply. Satoshi Nakamoto fixed the total supply Bitcoin at that amount, so, if you want to see Bitcoin becomes the primary currency, it is impossible. Unless you choose Ethereum or Ripple or other altcoins do not have limited supply or many coins at now.