Well, it doesn't have to have seen a lot of combat. It just has to have been a WWII plane. AH is a WWII game. Otherwise you've set a precedent that immediately opens the door for way too many more planes to consider.
That Australia was a minor actor isn't a snub, and admittedly the Major/Minor thing isn't how it works - it's like I said a quick and dirty way to categorize things. Australia's no less an authentic piece of the WWII air war than Italy and Finland. But when you have a plane that never made it to production, never mind put into action within WWII, and that's from a minor actor in the overall perspective of the war, and when on top of that the plane set is pretty lacking (lots of models that saw action from early to late war, many of them with production in the thousands) for two of the major actors in the war, it's just not an attractive choice for addition. That's just the reality of the situation, given HTC's resources. It's not about what I would or wouldn't fly. In fact the more planes added that anyone doesn't fly, the more rich the choice in targets to shoot down, the richer the environment to fly in.
And no, such a prototype from the major actors wouldn't be appropriate either, not right now (or ever, depending on who you ask).. Yes, lots of people would like a richer plane set.. No, the classic "major country" aircraft haven't nearly all been accounted for by now; that list of missing models is BIG.. And lots of people do care about one more Spitfire Mk.STXTIR. Lots.
All that aside though, you're right, there's no reason not to have that plane. I'm just telling you why it's going to be a long wait.