Isn't Bitcoin already addressing most of your concerns? I think the solution is not open centralization (Open source Banking) but de-centralization, which is what Bitcoin addresses by giving the power and money of the people back to people.
People won't "bank" when it comes to Bitcoin - There's no need of a Banking system really. And as per your concern around fluctuating value of Bitcoins, It's just a matter of how you look at it and standardization.
Assuming everyone tomorrow agrees to standardize that Bitcoin is the de-facto currency and decides to transact in BTC only, I don't think anyone will be concerned about fluctuation anymore. Item X which retails for 2BTC, will retail for 2BTC today, tomorrow and day after tomorrow. (Assuming no price change, offcourse)
Let's face it 'Assuming everyone tomorrow agrees to standardize that Bitcoin is the de-facto currency and decides to transact in BTC only' is a crazy assumption right now.
err consider John Doe... He doesn't give a damn if his bank is open source or not. John Doe is not your target, people who use BitCoins (and I don't mean lemonade selling girl scouts) are your target.
Electricity, Air travel, Internet? Don't you think these were crazy ideas some day?
With Bitcoin ATM's opening up in Toronto where I live, I see things moving fast than even myself expected. Sure, there will be resistance but it's hard to suppress something as revolutionary & crazy as Crypto currencies.
Assume the same John Doe :), ordinary internet user, Never heard of XYZ Open source bank, No idea how it works, 0 control over it. Will John trust his life savings with this Open Source bank?
I'm not trying to de-motivate you or diss you, infact I encourage everything Open Source! It's just that I'm attempting to outline that something out there already exists which solves may be atleast some of the problems you want to solve. Good luck!
Banking is about borrowing and lending. The idea that using bitcoin eliminates the need to borrow and lend money is something that could use support.
The idea & support for transactions like borrowing, lending, escrow and likely all other transaction types that you can think of are already built into Bitcoin & it's design. They are just not being used as of today.
Infact, I would say it's safer to carry out such transactions using Crypto currencies than with a Bank. Please see this video: http://www.youtube.com/watch?v=mD4L7xDNCmA
Satoshi was clever enough to think of all use-cases and he made sure that the design & eco-system would be solid enough to replace centuries old incumbents like Banks. The features are just sitting and hiding there in the protocol to be made use of when there is enough traction & momentum.