Great to see you post this and ask our special community!
I really like what ideas you have so far. To save time I think the best solution is to "crop" pieces of the full-scale map so we can fly on smaller pieces of it. (Not like the old "Online" maps where you only removed all objects outside the online-grid, but actually have smaller cut-outs that have no surroundings (like inf-flat terrain).)
A lot of beginners will appreciate the ability to takeoff and be in the action as soon as their wheels are up. These maps would also attract people with lower-end systems because they would require less resources.
In fact, perhaps a "sandbox" map consisting of two airfields and 2 small towns or something would make an ideal testbed for trying out new aircraft, features, missionbuilder things without excessive loading and required resources. I really appreciate the ability to have an "Empty" map for testing purposes!
So far the best idea of a smallsize 1:1 or 1:2 multiplayer map I can think of is just a small "channel" map. Have a little english coast, and a little french coast and you have the "Miniature battle of britain" map with water separating the teams. This allows a variety of missions ranging from anti-shipping to air patrols and raiding homebases/adjacent cities and or factories.
For the online campaign style maps, the full-size historical one would be sweet with 64v64 players
Just my two cents
