What makes Japan similar to Oberkommando. A lot of infantry from the cannon fodder - infantrymen to elite - paratroopers and marines,cheap tanks and very expensive prototypes. But Relic states that Japan can not do.
You're pushing into Maus territory though. Most of their prototypes were not used and were kept in reserve for the mainland invasion. If you want a fictional expansion of the US Invasion of Japan, sure, but otherwise I do not see them working well. Even that would be a stretch. Japan didn't have a bad military, they just put all their focus on their Navy and Air Force, leaving their Ground Forces under-equipped, and Ground Forces are CoH's only real focus with occasional Aircraft Support.