For me its the YAK3 and the KI-84 versions that are most lacking but the list is quite long and the only way its gonna get shorter is for these planes to get added.
Really?
There are a thousand versions of spits and 109s (because they are popular)
I'd imagine it's more because they were extremely varying planes that served from the first until the last day of the war.
The biggest holes in the Japanese planeset are probably A6M3, Ki43, J2Y, and G4M, and in the Russian planeset the Yak-1, Yak-7, I-16, and the Pe-2, maybe with the LaGG-3 and the Tu-2 tacked on there.
Of course a Fleshed out Italian planeset would be great as well, with a C.200 or G.50, CR 42 and an SM-79... and of course the Macchis we already have are in desperate need of update.
An MS. 406 or a D.520 would be nice for the French as well (the MS 406 also served with the Finns).