Fiat is the one that has given the best financial service for all our needs. If fiat is not there the system will collapse entirely, so fiat will rule the world even when bitcoin and other currencies increase in acceptance.
The bitcoin will also have good financial service in the future.
In future, it may be. But at present, the fiat currency is ruling the world. Anywhere in world fiat will be acceptable. But Bitcoin is not acceptable. And only in few place bitcoin is acceptable that too in only a few shops. But I too have hope that in future Bitcoin will become more popular and all country will accept bitcoin. But I don't have hope that Bitcoin will replace fiat currency.