Banks implementing a consistent API?
Having previously worked with banks (payment processing) the idea of the banks all implementing an API in a consistent manner is laughable.
They already have the APACS "standards" for transaction handling. Every bank implements it differently. Even if they did implement a common API they'd probably all interpret the same values in different ways leading to every consumer of the API having to put in special handling for every bank.
I've seen a bank implement it's own version of a standard inconsistently with their own documentation, let alone the standard itself.