100% impossible because bitcoin is not accepted by all countries and there are many country which are against bitcoin. and bitcoin is not the safest form of money because it has limit of 21 million so this would definitely cause crisis.
That limit is what makes bitcoin valuable. Without limit, it will be just another fiat that can be printed out unlimited, slowing losing value. But even with that said, it cannot make banks disappear. It is not designed to eliminate banks but just an option.
There are others altcoins with an huge supply and several new coins that after been mined can be staked and generate new coins, sure have a restricted number of coins should make it something rare, but some people already said that maybe bitcoin can cross those value in the future, meaning more bitcoin into circulation, i do hope they dont do such, but the core should do the best to bitcoin. Banks are following the world tendences, allowing several things to be done from phone at home, and their services are far away from what bitcoin can offer for you at the moment.
Yeah because banks in the first place is centralize while bitcoin is decentralize. In banks every transaction will have to go through the right procedure and it's not fixed because it depends on the volume of transaction and the amount of transaction.
In bitcoin it's fast because regardless of the amount transacted, we all transact in blockchain and the same as small amount.