Bumping. I'd like to know if anyone is interested in this thread still, and whether people think what I've wrote is plausible.
My opinion - I like it but I think the Chinese actions in the north (Mongolia and Manchuria) are unwise.
Elements in the USA were very pro-Chinese (or, at least, pro-business with China) for decades before WWII.
China as Germany's ally...well, the USA was very reluctant to enter the war prior to Pearl Harbour; combine the absence of Pearl Harbour with the vocal pro-China lobby and the USA might end up staying neutral despite Roosevelt's wishes.
As for a Soviet-China war? Invading China via Sinkiang or Mongolia would be...suboptimal for the Red Army to say the least. The existing railway lines, etc. run through Japanese controlled Manchuria. A reasonably competent Chiang or Hitler should be trying to keep Japan neutral while Hitler wins in the west and China ties down European forces by pushing into the Burma-Indochina region. Leave Japan for later.
With Japan and the USA neutral the Axis probably have the best correlation of force in the War they're likely to get. It all depends on whether the Soviet Union goes down or not.