He can not replace the fiat money, not because the price is not stable, but what is it is a deflationary coin! and people do not tend to spend it! all of our current economy is built on inflation is its engine! bitcoin is rather an excellent tool for investing, saving and accumulating capital, and not for everyday needs! in the place of fiat will come what is an alternative coin, it is not yet known which one) crypto-dollar for example)
That is right - using bitcoin to buy for just small things are quite not that wise because the price of bitcoin has really a good potential of increasing its price as time goes by. It is just really good for investment I think.