Making various transactions, either for goods or services is part of the activities of individuals and households. Obviously the utilization of the flexibility of Bitcoin for these transactions is on the rise, but something we're yet to experience, is using Bitcoin for micro transactions; gaming, online tipping, unlock assets of content creation, just to mention a few. For flat currencies, smaller units of the currencies may be in short supply to make such transactions. Households and individuals will surely be jumping at the prospect of the option of Bitcoin for these nature of transactions.
Mini transactions are costs that fiat can cover very easy, quick and charge less or equal to no fee. This is some of the reasons, i think those assumptions about Bitcoin replacing fiat totally are false.
Bitcoin as a payment option, is preferably a better choice when spending in large amounts, especially if the spending is across borders. Dealing on large sized transaction, spending fiat is going to charge more, time waste and following several due process, that makes Bitcoin reliable source for large scale transactions over mini transactions, fintech banks are the new order.