Bank could build upon 'the blockchain' to let me do a bank transfer in less than 2 days, or see my credit card transactions be cleared instantly.
It made some inroads, but a future alt-currency alliance would need to find very forward thinking technical leadership from within the entrenched industry willing to put their names into efforts of such an alt-currency alliance. Those players would need buy-in from the business and political wings of their organization. Where are the CEOs at banks and transaction network players who feel moving to a non-sovereign currency makes bottom-line sense?
Finding such value and leaders seems unlikely due to political relationships that the entrenched financial industry has. Put your name on an effort to remove oversight and control of the nations whose central banks you presently need at your own risk.
Unless the banking industry gets burned like the tech industry has in terms of the Snowden revelations and popular movement around privacy, there isn't an obvious self-interested basis for taking on this sort of risk.
My general point was that I imagine most banking systems are legacy and archaic, and if they ever wanted to improve them Bitcoin could be s potential implementation detail for a modern system.