No bank will ever accept any currency without commission From now on they take an interest at a reasonable rate Fiat takes commissions from now on due to currency centralization but in the case of Bitcoin it is never possible.
It is possible if you let the bank take care of your bitcoin with insurance and this might be the most likely to happen with mass adoption for bitcoin. If banks would dare to get into bitcoin, they will take the risk to do so giving their full accountability in exchange for trust with the cryptocurrencies. Commissions on bitcoin will be high that's for sure given banks will risk a huge part of them just to get long with the trend, besides if it clicks massively they will get a huge profit out of it. Just in case it happens
If the banks can't provide Bitcoin security then no one will deposit and the demand of the banks will decrease Without adequate facilities the exchange will become much more difficult.
Security in terms of technology, there is no more secure facility of money in the online but only crypto, what's not secure is the 3rd party services. I think bank will also run after the blockchain, they might introduce a new technology, an innovative blockchain, how is that for the security?