Its impossible it will never happen because every human being has their own potential and have their own skill to do job and not at all are interested to do it although in bitcoin it helps financial problems and also bitcoin never threat to national currency because every country have their own currency with rules and regulations.
Yes, it is very impossible to happen and cryptocurrencies and fiat currencies both have their own ways of use. Also people can have their ways and strategies to be able to earn both of it.