The XII would be a great addition (after the Japanese and Russian fighters and German bomber quotas are complete) because it was the step in between the Merlin and Griffon Spitfire variants. It was the Frankenstein (Yes, I know Guppy

Don't hurt me) of the bunch and was literally a Griffon with a plane strapped to it.
The Seafire L III would be a good addition because it was the most common version of the Seafire and it was built from 1943 - 45, the longest serving Seafire available.
The Spitfire Vc is my favourite version of the SpitV but it simply was not the most common Mk.V. The MkVb was byfar the most common and hardest working of the bunch. As much as I would like to see it, it will never be added unless EVERY single plane that ever fought in WWII was added.