Now that the game officially includes NRA troops, there are no more excuses not to include the largest front of the war - the Far Eastern front.
The Chinese faction should be more than large enough to stand alone, with a variety of units from local militias (29th Route Army), German-trained NRA troops (88th), and Communist forces (8th route army).
BR I and II of both Chinese and Japanese factions can be supplemented with cavalry units, which would function similar to motorcycle troops but with a strong melee attack instead of machine guns. The campaign could also expand on melee combat, since both factions widely used swords. Poison gas would be another great addition (basically the same mechanic as the current white phosphorus grenades).
The map itself could offer some good diversity as it would be the first beach assault into a dense urban area. A secondary map could include the Nanking route.
The Burma campaign could be adjusted to allow either the allied faction or the Chinese faction to fight against the Japanese, at random. This same mechanic could be used to regroup the residual Axis powers into their own faction (Italy, Romania and Hungary), which could replace Germany at random in the Tunisia, Stalingrad and Rzhev campaigns. With their own uniforms this time, of course.