First of all, it is necessary to have a lot information about a plane prior to model it. So, I suppose most of the planes we are talking about are out of scope.
I think that AHT should model as many planes as they are able to, except those that never enter into combat with enemy planes.
Having a me262 or me163 is a good idea, just to recreate the real WWII engangements. The main arena could be divided in three year sets: 39/41,42/43,44/45, filtering the available planes for each one except for 44/45 period.
From my personal point of view, I would designed the arena as follows:
1 - Three year sets.
2 - Two teams: axis and allies.
3 - Two scenaries: Europe(east,west and mediterranean front) and Pacific.
This way there are six sub-arenas historically tuned.
To make this possible we need more Pacific fighters, transports and bombers. Also more german bombers and transports and perhaps even figthers (190A3, 190D9). I think that several versions of P47/P51/P38 are also a must as well as hurricane and early Spit versions. I know, I know, I'm asking for a lot, but the very hard enemy to beat is just WarBirds, did you remember?

As a side note, it could be a great idea to have strategic targets like factories and fuel depots whose destruction could imply less % of fuel at the bases and less bombs and rockets. Radio coverage is another important factor.