Apple doesn't need to be the bank, just control what the banks have access to. Apple could parse out what it means to actually be a bank. Working Capital (or day to day bill paying) is different than long term savings, lending, investment accounts, and all the other retail products they are trying to invent. Each is a commodity service, but billing has a significant streamlining/comptroller opportunity that could be helpful to Apple's profitability.

The banking and payments infrastructure is such that most of it is handled by intermediaries and other companies anyway. Most banks, for instance, do not issue their own cards or process their own payments - this is done by an intermediary. It's probably easier for Apple to break into banking by making the right partnerships than you think.

They already have the partnerships in place with ApplePay, I don't think they would every want to open themselves up to the type of scrutiny/regulation chartered banks face