Well I'd like to see the Brit. CV aircraft fleshed out a little. Either by a carrier born attack plane, "Firefly", or a later version Seafire. Maybe that late war one with the Griffon engine.
Think about it. Out of three major CV builders and operators in the war we have 4 Japanese CV aircraft included in the game, fighter and Jabo, at least 6 Yank ones, and only 1 Brit one/United Kingdom. Which wasnt really a CV fighter at all.
Other then the D4Y I dont see much else IJN-wise that set has to offer. The exception being possibly an IJN CV itself, which would be awsome. Shokaku class please, or Akagi.