Well, light tanks for both sides could work well.
3) No Japanese armor, impossible to balance
4) (most importantly) At least it's kind of vaguely conceivable to see USSR and USA on the field together. But you would never ever have any other factions besides USA and Japan, thus no separate armies for DLC etc.
I think adding Britain or China as a DLC would still work since they fought the Japanese. On the Axis side, it seems like only Japan will be suitable.