You have an interesting question but why would a big bank need Bitcoin principals? Why would they need a blockchain?
They could just create Citicoin in their databases around the world. No need for bitcoin or a blockchain for them to create a virtual currency.
Unless I am missing something?
An internal blockchain would prevent against casual employee theft, and double spending, etc. It is secure enough that it would be imposssible for someone to counterfeit. Besides the closer their product is to bitcoin, the more successful the attack...whether actually getting the trademark or just creating confusion about bitcoin.