China is extremely worried that the dollar will depreciate; that's why it would ideally like to hedge itself more broadly. That's the entire problem it has to deal with, the risk that the dollar might weaken. Suggesting that China is looking to "kill the dollar" is ass-backwards, China is worried that the dollar will be weakened since nobody is more exposed to that financial risk than China is. So it's in an awkward position where the US has every incentive to weaken its currency and fuck China over.
This is particularly true now that the US has recently become the world's dominant oil producer due to fracking, and no longer needs to buy foreign oil (the main import you would want a strong currency for).
There's a common misconception among economic CTs that "strong currency" is what all nations want, because it defines national power. This is where things like fiat currency, fractional reserve banking, the gold standard, and hyperinflation keep getting cited. But it's completely incorrect. Much of the time countries are battling to weaken their currency, and to fight off forces that would strengthen it. LIKE CHINA ITSELF IS DOING by keeping its currency artificially weak, on purpose. As is the US, which prefers a softer dollar. The story of the China v. U.S. currency position is that both are trying to devalue their currency and force the other guy's currency to rise in value. The exact opposite of the currency CT world view.