In fact, regular money took long to be used in its electronic version. I still know people that do not trust much on online bank transfers and payments. Due to Bitcoin being full online, well, it will take some time.
I am happy if it is a way to store value for some time.
I don't think even after Long time it will happen. Very difficult to replace the existing currencies with Bitcoin.
Bitcoin will coexist with existing currency for a long time. Fiat is easily printable by governments so goverments like it.