There already is an open banking API: Bitcoin (Score 1)

Bitcoin is the open, decentralized and open-source banking API.

Despite what you may have heard, the technology is thriving and the number of developers, projects and startups in the space is exploding. 2015 is on track to be a $1b investment year for bitcoin, most invested in USD (not bitcoin) in more than 700 startups.

It's a lot more than a currency, it's the Internet of Money, or Money-over-IP (MOIP). Read the Satoshi Nakamoto whitepaper, every geek should.