I'd like to see the Ki-44 brought in as a high-alt bomber interceptor.
I like the Ki-61 as it is, but would be nice to have the option for four 12.7mm guns to improve climb and turn for turnfighting. The Ki-61 with cannons makes a nice downhill boomer. Would the Ki-100 have improved speed and climbrate?
If the Ki-84 were introduced, would it replace the n1k2 as the ultimate IJ plane?