There are a couple of fascinating assumptions recurring here.

First, even assuming (though it's very questionable) that China is bent on storming out of its borders and acquiring new territories, either through conquest (less likely) or by absorbing them into a sphere of influence (more likely), why do we assume that this ambition would be directed into the Pacific and in the direction of the US? I'd think it far more likely that such an ambition would be directed toward prying Central Asia out of the Russian sphere of influence and into a Chinese sphere. I'd think over the next few decades China/Russia conflict, with Central Asia as a flashpoint, would be more likely than conflict with the US. If you were China and intent on gobbling somebody up, why would you gobble SE Asia when you could go for Kazakhstan (30 billion barrels of oil, 85 trillion cubic feet of gas) and Turkmenistan (265 trillion cubic feet of gas)? Not that I think China is likely to invade these countries (or SE Asia), but they could definitely try to move in offering resource deals, trying to build political influence, and generally trying to supplant Russia as the dominant power and the dominant resource outlet. Russia is likely to object. Where that goes is anyone's guess, but there's certainly potential for conflict, especially since there's something tangibly worth fighting over.

China's next external military venture may not be a neighborhood conquest. There's a real possibility that China could end up in a FID/COIN situation if a compliant government protecting major Chinese investments is threatened by insurgency, especially if that insurgency takes an anti-Chinese position. Most likely scene would be Africa. Hard to say how China would respond to such a situation, but it could emerge.

Again, all of these are speculative (as is the assumption that Chinese aggression in the Pacific is inevitable), but the assumption that west into the Pacific is the sole or most likely target of Chinese military development is certainly questionable.

The second questionable assumption is that conquest or expansion are primary agendas for the current Chinese leadership. This site by its nature focuses on the military side of things, and it's easy to forget that the primary business of China is still business and that China's economy is heavily dependent on trade. While China's leaders will undoubtedly push and shove as far as they can without provoking actual conflict, I think it most unlikely that they have any desire to push to any point that might rock their economic boat. It's also worth noting that the economic boat is not nearly as stable or secure as it's sometimes claimed to be. The Chinese government's management of its primary security threat - its own populace - has been heavily dependent on the ability to generate continuous economic expansion, and that's getting harder and harder to do.

The current dispensation is not ideal, but it is manageable. The single biggest thing to fear, for me, is that a serious internal upheaval (a very real possibility if economic problems emerge) could result in the emergence of a hardline communist/militarist government that aims to purge all those effete capitalist businessmen and get back to ideological purity.

Again, all very speculative, but the assumption that the current Chinese regime is necessarily bent on conquest and expansion definitely needs to be questioned.