Retail, the balance problem is that no one wants to fly a zeke against a hellcat. Also for early war events, there is a serious lack of variety for the Japanese. For instance, this is what i proposed for a Solomon islands campaign, one that progresses like BoG
USN:
F4F - F4U-1 - F4U-1A
SBD - TBM (for SB2C)
USAAF:
P-39D - P-38G - P-38J
B-17G
B-25C
RAAF:
P-40E - F4U-1A
Mosquito Mk. VI (later frames for beaufighter)
IJN:
A6M3 - A6M5b
D3A
B5N
IJAAF:
Ki-61 (later frames, max 12 aircraft)
G4M-1
You see there is a major lack of variety, and this is the best I can come up with. I don't think there would be a whole bunch of appeal for the Japanese side, because I for one would not like to fly a zeke against corsairs, p-38js and mossies.