I believe banks will always be around and that at least the US will always be on a fiat system. I'll be interested to see in the future if any banks will allow the storage of both fiat and cryptocurrencies with the ability to easily exchange fiat to BTC or BTC to fiat without leaving your bank account. That certainly won't happen anytime in the near future. But I'd be interested to see what changes are made to banking in the next 20 years.