I think as of now, because not everyone has access to Bitcoin and bitcoin transactions, we will not see it take over fiat for a while. With bitcoin, every person will need some form of device that allows for transacting money. A lot of the population is in rural areas, are poor, and may not even have access to things like electronic devices. For now, fiat offers a simple, well accepted currency based on a country. If we can get to the point where everyone has an electronic device or that every government provides it, then only will I see it possible for bitcoin to take over.