Alternatively, could Japan reach reproachment with Europe for a piece of the Chinese pie if they end up dawdling long enough? After all, once he's subdued the Warlords Chaing's next target are those exact European concessions, in which she's supported and aligned by the other powers seeking revisions to the post-Versallies order (The USSR and Germany). Britain and France's colonial security is just as threatened if not more so by a China waving the anti-European banner as Japan, which is a fact Tokyo could leverage to restart warm relations with Britain, to back when they were allies
Japan's stake went up as it filled the Russian vacuum, as the Great War raged they courted Russia as the new ally to offset American strength as they saw it growing and becoming a threat to Japan, with greater Anglo-American cooperation Japan already felt left out or sacrificial, cemented by WNT, and Japan really turned its outlook once it took Tsingtao from Germany. This left Germany (and A-H) without any concessions or footholds, thus Weimar aligning with KMT versus Japan is logical. Just as the revanche USSR aligns with KMT to offset the "Capitalist" powers. The USA has concessions but no territory in China, her delusion is she is above the Unequal treatment and fairly pursues an Open Door. Thus the USA is not wholly in the British/French camp but clearly not in Japan's. China was a loser at Versailles like Russia and obviously Germany. Japan got snubbed later. Italy did not get what it wanted. The pattern is set. China was a significant place to earn profits, most of all for Japan, it could be for a Germany acting outside the old set-up and she has nothing to lose disrupting things. Long-term Weimar was more likely to run up against the British and French who had the most to lose. A stronger Britain should pursue suppressing the KMT, containing China and reducing Germany's aid to China since that is easier than stopping the USSR.
I think Weimar could be bought, Japan would be less aggressive with Britain exerting more power in Asia and the USA will not exactly back Britain but will support keeping Japan in line. That leaves the USSR, as things go on the Europeans likely do see anti-communism as more vital than retaining Versailles, Weimar will get let back in the camp and Japan too could retain more for less as the anti-communist bulwark to the East. China remains the loser here. I see how her best bet was Weimar, not strong enough to kick China down and capable of modernizing her, the only European power willing to benefit China aside from the USSR but they could put designs on China and are a very dangerous ally. For me the question becomes how does Britain turn Weimar back to exploiting China in ways that keep China down rather than make her stronger? And with no genuine threat from Weimar how does Britain actually shift focus to Asia and wrestle with Japan. For me the USA is only a danger if provoked, so long as Japan does nothing overt she simply gets pissed on but has nothing more to fear.