I will make my arguments as to why don't want the Japanese faction in the game.
The faction would primarily be focused on infantry, they would bleed manpower like a stuffed pig. Just like the USF. This would be difficult to balance a faction with a majority of its units being infantry.
Don't even mention the tanks, because they wouldn't last against three SU-76s or even a T-34. They're anti-tank power is somewhat limited since it is very close to the M-42.
While traps would be interesting, the British would have their mortar emplacements and Mattresses to light them up. There is also the Churchill Crocodile to mention...
Another factor to take into account is that air power for the Japanese could be limited since the allies have the Centaur, AA M15, and an M5 to counter it.
Then there is also Relic themselves to factor in. They're still trying to fix the issue of Volksblobs which has plagued the game since WFA was introduced. Not only does it end there, but they now have a Collection Edition on Steam. From what that suggests, they will only focus on balancing the game since it looks like they're finished with additional content.
Not to mention that if the Japanese would be included, those who play the Men of War series will think that this game is trying to be like a wannabe Men of War with 'arcade' features.
There is also the matter of being an overpowered faction at release and the nerfs afterward. However, the future may be bleak for this faction since there is a possibility of ending up on life support. The Brits are a living example since they used to have that status.
