I cannot see how China will supercede the USA as "the" major superpower in my lifetime. China is effectively being turned into a mafia state - many private businesses have had their assets stripped by people who are effectively gangsters, using government levers to make these actions "lawful". It seems to be mirroring what has happened in the old USSR, just as it did when Mao rose to power. The Wikileaks cables made it pretty open what everyone knew - that Russia and a lot of the old USSR are now mafia states - China is now following suit.
There are still large parts of China's economy that still work as a command economy, and thus still sectors of it that are hugely inefficient.
Fair enough, the USA owes China (and Japan) a humungous amount of money - but China owes much of its prosperity to the USA. Without the USA they wouldn't sell a great deal of the goods they have. Without the USA there wouldn't be the "boom" China has experienced in recent years.
Don't get me wrong - US government policy has effectively shipped a stratospheric amount of money out of the pockets of US citizens and into the coffers of the Chinese government (and now Chinese gangsters). China's fixed exchange rate hasn't helped things in that regard. But the US economy is far and away the world's largest - and China's isn't going to match it anytime soon if the current situation continues over there for any length of time. As Italy has found, once you let organised crime in, it's awfully hard to get rid of them, and your economy and ordinary citizens will suffer as a result.
Anyway - I figure the globe is in for a significant deflationary period at some stage very soon, and that will affect everyone - probably the Chinese the most because they are the ones who have been rewarded the greatest through the absurd US government policy of deliberate inflation over many decades.