From a wargamer's perspective, this sort of speculation has some interest, if only because China is about the only power that could, theoretically, be considered anything like a "peer competitor." That is, it's about the only potential foe that would pose any sort of challenge involving conventional warfare. A war with Iran, in contrast, while more likely, would mostly pose unconventional warfare challenges for the US, much less fertile ground for wargamers, especially those interested in naval affairs.
On the other hand, from a political standpoint a war between China and the United States seems highly unlikely, but also would probably be an unmitigated disaster should it occur.
As Edward Carr noted here:
"The tripwire for outright conflict might be trivial: a scrap between China and one of its neighbours over some islands, or a miscalculation as American warships sail up to the 12-mile limit that defines Chinese territorial waters. But when the dominant male and the pretender square up, everything about them is at stake. Just as two conflagrations burnt the heart out of the 20th century, so a war between the leading powers of the 21st could set off an orgy of destruction.The shadow of nuclear devastation is one reason to be fearful. But even if we avoided that last, hideous step, the cost would be immense. That is partly
because today’s conventional weapons are so potent, but also because China and America depend on each other in ways that Russia and America never did. The flow of goods to our shops would dry up, as globalisation failed. The financial system might collapse, because America could not borrow from China, and China would have nowhere to put its savings. Cyber-warriors might wreck communications and infrastructure. Collaboration on trade, science and action on climate change would be swept aside. Global economic depression would drag billions back into poverty."
Now, clearly the fact that a war would be a colossal bad idea is no guarantee that it won't happen after all. One only needs to remember the summer of 1914 to know that it can happen anyway. But neither country seems very interested in stoking tensions at this point and I'd rate the chances as being rather low at this point. What the situation would look like in 20 years, or even 10 years, is hard to say. A lot can happen in that amount of time in politics. In 1923 Hitler was in jail for the Beer Hall Putsch, a decade later he was chancellor of Germany and a decade after that was embroiled in a global war. Clearly few prophets in 1923 would have foreseen 1943. So caution is warranted. Still, wars between global powers usually turn on identifiable clashes of interests and its hard to discern what those might be in the case of China and the US. Much of the great power rivalry of the 20th Century turned on ideology -- one sees no great ideological rivalry between the US and China. There are always possible geopolitical clashes of interest, as seen in the first half of the 20th Century, but it's hard to see much of that in the US-China relationship. China' disputes and concerns are very local. Even the Taiwan situation doesn't really represent a clash of interests, really. In large part it's a dispute left over from the Cold War. A Chinese invasion of Taiwan now would not have the same implications that a Chinese invasion of Taiwan would have had in 1980.