Basically, a US-Chinese alliance would have huge military, political and economic clout, with an interest in preserving the status quo. It would definitely benefit Australia, who is politically close to the US, but economically closer to China. Pakistan would probably have to join, if for no other reason than being an ally of both the USA and China, and to exert pressure on India. South Korea, Indonesia and the Philippines would likely be involved too.
Of course, nothing is set in stone. The US will probably drift into opposition with China...the "pivot" to Asia is proving to be a destabilizing influence, with its unspoken assumption of containing China causing China's regional foes to scramble for reasons to push their agenda onto the US budget. You know, like the last decade in the Middle East, writ large.
But right now, if I were looking for longterm security risks in Asia, it would be Japanese nationalism, militarism and rearmament allied with a nuclear India and a potentially nuclear Burma, with a revisionist understanding of the history of the region and antipathy for both the US and China.