Yes true, bitcoin will never replace fiat, this is because the state protects fiat like protecting other state assets, it is strange if we think that bitcoin replaces fiat while many things become bitcoin big job eg problem of the transaction speed.
The fact is that not because of Bitcoin transactions may not take place Fiat in the financial world. The fact is that many people will not be able to use crypto currency as a means of payment, because they do not have the opportunity in the Technical Plan, while in others there is not enough knowledge.