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.
I do not think guide how to use Bitcoin is more difficult than find a good price to sell Bitcoin. Bitcoin trading can takes some fees for transaction, beside that, its demand and supply on the market are not fixed. Demand and supply are always change everytime. More demand, you can sell Bitcoin with good price easily, but low demand, you can need to wait a long time up to few years to sell Bitcoin at what price you want.