Might suprise you to know...
There has been a push to add Japanese Ground Forces for a long time, and a Japanese tank historian has documented every Japanese tank built and developed. With his help they worked out what the tech tree could look like, and its a surprisingly full roster.
http://japangroundforces.weebly.com/
Granted this is slightly dated now that Jap GF is already confirmed, but the tanks are all there.
Besides rounding out all the nations in game with their own ground forces, Japanese GFs let us see what tanks Japan really did have and what they came close to having. British tanks are a perfect example of the fact that armor doesn't mean everything, especially when you have armor, firepower, and maneuverability advantage. From high tier to low tier, armor is very much irrelevant between vehicles of the same BR. More often then not, each vehicle at a given BR will have a round that can cut through the thickest part of another's armor, and even taking into account armor angling you will almost never be able to always have the perfect angle to bounce everyone's rounds. Perhaps a TD or higher BR tank puts a stock round right through your front, or you get flanked n spanked, armor angling doesn't help at those times. And even if you do find yourself at this perfect position where you can bounce everyone's rounds and you aren't flanked or facing higher BR tanks, all it takes is one strike from a plane to put you into your SPAA.