Ki-43, Ki-44, Ki-45. Also, a J2M so the IJN doesn't feel left out.
Hell, even a Ki-27 for the I-16s! Khalkin Gol scenarios! Now that we know biplanes are possible... an I-15 to make it even cooler

CR 42, MC200 and we can recreate early Med/North African scenarios. We can recreate em better if we get a Gloster Gladiator and Fairey Swordfish too!
Seriously, I'm thinking all the late-war uberbirds have pretty much all been added. There isn't anything left that will see serious use.
Flesh out the planeset, or flesh out the ground game. I'd rather see the planeset, but I'm a walking, talking anachronism.