yup, because fiat was never be removed in a certain country because technologies never spread so fast on every person by the cause of poverty. Still cryptocurrency not accepted by some country that's why it will never replaced a bank by a block chain.
Never is a word that is used when something cannot happen in the real of forever. Digital currencies are still too young and you must have seen that the number of people has increased over the last few years. So these coins have already started to grab fame and become a hot topic for top governments of the world too. It is just a matter of time before bitcoin will go mainstream and fiat will be wiped out.
You are mistaking the question here. The question was not if Cryptocurrencies are success or failure. But the question was Can Blockchain based currencies replace banks and the answer to that question is NEVER! Cryptocurrencies and Banks are not even closely related. It is like comparing apple with strawberry jam. Bank is the institution that provide services like loan processing by accepting collateral which are standalone not at all possible with cryptocurrencies.