I think lots of people are banking on what I call the "Fukuyama thesis" re: China, which I understand to be a general skepticism about China's ability to seriously challenge the US for the following reasons:

1.) Basic cultural (or perhaps innate?) differences which predispose the Chinese towards low risk behaviour and conformity. The basic claim is that catch-up technological progress is different from progress on the bleeding edge and that the Chinese are better at the former than the latter. From what I understand, there may be some truth to this, although it's exaggerated and also complicated by the fact that many of the major breakthroughs in the US are the result of work done by immigrants from China, SK, etc.

2.) A lack of responsive institutions and the absence of checks-and-balances on government exercise of power. Fukuyama and his comrades thinks this cuts both ways I think; when China has good leaders, the upside is amazing because gov't projects are expeditiously completed, but then you also have to deal with the Maos. Someone like Zhang Weiwei would probably counter by noting that China has built informal norms through the Communist Party that emphasize promotion based on merit; I think this is compelling, although I'm still not completely sold.

3.) Long-term demographic problems. Unless I'm mistaken, China has a massive long-term problem with dysgenics. Also, if China's trajectory is anything like SK or Japan, young people are going to have real problems with under-employment, diminished social mobility, etc. The social mobility thing is probably a big thing in China in the long-run; I read some interview by a Sinologist that like => 90%people who have seen the largest gains in China are those whose lineage can be traced back to Qing aristocrats. (This is premised on the assumption that the socially immobile have the social capital and the desire to mobilize though; from what I understand, rural areas tend be the most conservative and exhibit the staunchest support for the party.)