In my opinion, the MA pretty much has all that it needs especially in terms of fighters. Though there is a great choice of planes available to the player, there are a few planes that see an overwhelming amount of use. The Hurricane and IL-2 should be great ground attack aircraft but you hardly see them and that's because even during the real war, no one would've sent them into a situation that is the MA. And this leads me to thinking the P-39 would not be used all that much in the MA...it would probably just thin out and compete for time those types already being used by those few brave souls who will take up a lesser ground-attack aircraft. In the MA with the P-39, Hurri, BF-110 or IL-2, none of these planes are great air-air or pack a huge air-ground punch compared to things like the Typhoon, F4U-1C, P-47, P-38 and Mossie and others that have good guns and can carry a large ordnance load. The MA will always see the greatest performing (late model) aircraft overwhelm the other lesser types. And this leads me to forecast an evolution with Aces High. The Special Events and the Combat Theater! (Well, I can hope at least.) Maybe now is the time to start introducing aircraft in theme-packages. It appears we may see that soon with a Battle of Britain set including another Hurricane, another Spitfire, another 109 with an added BF-110. Sure, you'll see these aircraft on occasion in the MA, but it's not going to have any real affect. If the P-39 is added, and I hope it is, it should probably come with a set that includes the P-40, F4F Wildcat and maybe an early P-38 and certainly an A6M2 and A6M3! Odd we have so many 109, 190, Spit, Hurri variants (two Yaks, two LA's, 202 and 205) with just one P38 and Zeke! Anyway, I had a few minutes on my hand and I guess I wanted to thrown some words this way.
I look forward to the BOB set and hope to see an early-Pac set one day too.