Banks are not into existing cryptocurrencies that is for sure. Banks are the number one enemy of decentralized currency why would they adopt it? and talking the volatility of cryptocurrencies, banks having an uncertain edge will never be in place. New stable coins will be created for them, a well regulated and backed coins.
Why would the banking system consider the decentralized currency an enemy,they will be getting business from exchanges because if you want to purchase these currency you need the help of the banking system to send money and that means the banking system will get business and all they will be looking forward is business and if there is a clear regulation by a government then i bet the banking sector will not have any issue dealing with the crypto exchange.
You are only thinking in the way things are now but not about how things could be in the future if cryptocurrencies become the massive success that we expect then people are going to stop converting their cryptocurrencies to fiat to make transactions, they are going to deal with cryptocurrencies directly and when that happens neither banks or governments are going to get any revenue from those transactions, even if a low percentage of the transactions of the world begin to go through cryptocurrencies this will create a lot of problems for the governments.