Think of bitcoin as gold and the online bitcoin banks as all the currencies in the world. I'm going to hold more of the currency that stays truer to the nature of gold.
I don't know how the interface would work, but I'm sure someone already figured that out.
This is precisely one of the reasons why advocates of a central monetary authority (like the Federal Reserve) want to keep a unary legal tender.
You can't arbitrarily inflate or manipulate a currency when there is no barrier to using other currencies.