I don't think bitcoin achieves anything that those large organizations actually desire, if credit card is faster and more secure than Bitcoin why would they be interested? I think you'll find any large organization is quite happy with the status quo when it comes to financials. They bend over backwards to interface with the existing banking systems as these banking systems are heavily invested into them.
Well, here's the thing, it's not faster, it's not more secure and it's not cheaper than bitcoin. Many industries are turning over close to 50% of their earnings to the banking industry. Retailers that operate on very thin margins are very interested in alternatives to the legacy banking system.
As soon as bitcoin is a threat, or a perceived threat, these banks will throw money at it and shut it down with a 51% attack. 5 million dollars is nothing to these people. Let alone governments. The only answer Bitcoin supporters have is things like "p2pool" or "one day we'll be so powerful they'll need 50 million dollars" . This isn't a real answer to that question.
By my calculations you would need a couple hundred million right now to mount an effective attack. This is taking into consideration the very power hungry data center you would need and all the construction costs. You might even need to build a manufacturing facility to crank out the number crunching hardware that you'd need (that will push your costs up substantially). You may well succeed in destroying bitcoin. But then you have litecoin and all your massive investment rendered useless. All you need to do is tweak the proof of work algorithm to render any such attempt an exercise in futility. You might disrupt or delay bitcoin (or an equivalent successor), but you won't, in the end, stop it.
I think any bank or government that seriously studies bitcoin will ultimately arrive at the analysis that the bigger existential threat is in ignoring or trying to stop bitcoin. Any government that cracks down on it will not succeed in stopping it and simply push the investment and innovation into bitcoin overseas. They may in fact be cementing their fate to a future as a third world country with such action. My biggest concern is that people in position of power will make rash decisions out of fear and ignorance to their own detriment and the detriment of their citizens.
And, no, you don't need need a cooperative banking system for bitcoin exchange to continue and even thrive. A p2p exchange system could operate entirely in the absence of any bank accounts. The better play would be for the banks to try and regulate the existing exchanges because if they cut them off, they'll lose any possibility of control.
My advice to banks would be to start using and learning about bitcoin now. At the end of the day, it's just a piece of software that tries to invent a better, more secure way of implementing money by taking advantage everything we know about cryptography and the internet. It's stands to reason that we can do better than the legacy system that has been cobbled together over the past 40 or 50 years and which is full of inefficiency and security holes.
My advice to government would be to start mining and buying bitcoin now. And start thinking about the future when you'll need to enter into treaties with other countries concerning the amount of hashing power they agree to devote to securing the bitcoin network (and stockpile some hardware in reserve just in case some countries try to cheat).