The argument that IDNs will take off as China's economy grows doesn't hold much water. Japan has a strong economy, a non-English speaking population, high levels of usage of their ccTLD, high per capita income, and all sorts of other things that should make it a prime candidate for IDNs. So where are all these IDNs they should be using? Clearly there are other factors holding up the widespread adoption of IDNs.
The main problem with IDNs is that very few applications support them. Oh yes, I know IE7 will change the world! Yeah, right. I'm sorry, but until every major browser, email client, and other Internet application supports IDNs they aren't going to take off. Without a lot of IDNs in use the incentive to add this support to an application is low. Chicken & Egg.
It's likely we'll get there eventually. We'll reach some point of critical mass where they just take off. Hopefully within my lifetime. Hopefully before the DNS system becomes obsolete.
If Chinas economy can continue growing at the current rate for 50 years it will indeed surpass that of the US. Of course by then, all life on earth will have been extinguished by their toxic cloud and the weather forecast for the forbidden city on Christmas day will be a balmy 100 degrees centigrade with a chance of sulphuric acid showers. IDNs won't be worth much of anything then, so lets not count on China's economy to drive IDN values