According to the BIS, the US dollar made up 84.9 % of currency turnover in 2010, down from 89.9 % in 2001. The yen also declined.
The Australian dollar, acting as the international currency best representing growth in Asia, went from 4.3 % to 7.6 %. The renminbi is at 1%.(1)
Given its internal poverty and disparate geography, the centralized control of currency value is a matter of survival for China from the perspective of the CCP. A currency float and a liberalized financial sector would probably break up the Chinese banking system and with it the power of the party.
As Kenneth Rogoff writes: "Clearly capital flows can be used as an excuse, as they are in China and India, for financial repression – to protect domestic financial services sectors from competition and retard their development".(2)
(i.e. let Goldman Sachs be free.)
How much longer effective capital controls can last given China's integration into the trade of goods and raw materials is an open question. Internal and external political pressures would seem to building in the other direction.
1'Triennial Central Bank Survey' - BIS
2'Tensions Rise in Currency Wars' - Financial Times
Note: Currency turnover percentages add up to 200.