Interesting. Not a bad story.

I couple things to consider.

China has overtaken the U.S. GDP in terms of PPP (purchase parity power, or how much goods and services their equivalent currency can buy),

The U.S. is not really the worlds leading economy.

The Dollar will eventually be dethroned but it will not be replaced with one currency. I will be more like replacing a monarchy with a democracy. A bigger variety of instruments will be used for money transfers. That will actually be more efficient, why should other currencies need to be converted to dollars for international trade. China as a lot of Euro's coming in as well as dollars so why not spend the Euro's as Euro's and not convert them to dollars. It would seem no big deal to me that China might accept rubles for trade since they need to buy Russian gas. Most trade will still be in dollars since the rest of the world does not have enough bilateral trade to stick to their own currencies.