Bitcoin cannot replace fiat, as long as taxes have to be paid in fiat.
Once bitcoin is accepted and respected by the state then it will be the start of a new era.
Otherwise, we can have a bitcoin economy slowly develop. Smiley
Fiat is the most powerful currency and bitcoin is simply inferior to bitcoin because it's just a payment system, I doubt even if it will be very popular it will surpass the success of fiat. I mean, fiat is widely used because it was endorse by the government and we trust our government to govern us, with fiat the circulation is properly accounted therefore we cannot do away with paying taxes which is the life blood of a country.