...they just gave it a funny name, the bancor
From
http://en.wikipedia.org/wiki/Triffin_dilemma:
"The Triffin dilemma or paradox is the conflict of economic interests that arises between short-term domestic and long-term international objectives when a national currency also serves as a world reserve currency. The dilemma of choosing between these objectives was first identified in the 1960s by Belgian-American economist Robert Triffin. He pointed out that the country whose currency, being the global reserve currency, foreign nations wish to hold, must be willing to supply the world with an extra supply of its currency to fulfill world demand for these foreign exchange reserves, and thus cause a trade deficit.
The use of a national currency, e.g., the U.S. dollar, as global reserve currency leads to tension between its national and global monetary policy. This is reflected in fundamental imbalances in the balance of payments, specifically the current account: some goals require an overall flow of dollars out of the United States, while others require an overall flow of dollars into the United States.
Specifically, the Triffin dilemma is usually cited to articulate the problems with the role of the U.S. dollar as the reserve currency under the Bretton Woods system."
Keynes argued that a national currency could not function as the world reserve currency for exactly this reason and proposed the bancor, a supranational currency, to solve this problem. Unfortunately the idea died with Bretton Woods, but in 2010 the IMF revived it:
"On April 13, 2010, the Strategy, Policy and Review Department of the IMF published a comprehensive report[6] examining these aforementioned problems as well as other world reserve currency considerations, recommending that the world adopt a global currency (bancor) and that a global central bank be established to administer such a currency. In this report, the current issues with having a national global reserve currency are addressed. The merits, difficulties and effectiveness of establishing a multi-currency reserve system are weighed against that of the SDRs, or "basket currency" strategy, and those of establishing this new "global reserve currency". A new multilateral framework and 'multi-polar system' for managing capital flows and national debts is also called for, but the IMF cautions that it prefers a gradual shift to this new framework, rather than a sudden change."
Moral of the story: next time someone tells you Bitcoin is a libertarian fantasy, point out that Keynes and the IMF would love it if the world ditched the USD for BTC.