1. WWII condensed into a tour long war with a starting date of september 1939.
2. Introduce a Rolling planeset in which planes become available when the date of the arena matches the date of the first known missions of said plane.
You run historic scenarios according to arena date by simply changing to the scenario terrain and picking the planeset for the duration of the event.
Once map is won after the scenario terrain, the terrain random generator goes back to work and the rolling planeset picks up where it left off.
This would require very little administration other than running the historic events within the arena and setting it back on "auto".............which is the job of whoever is running the event.
"Events" don't have to occur unless someone wants to run one and, since history of WWII is already known, it is easy to divine when a event scenario will occur within the timeline.
All you have to do post a list of events in the forum.........the dates are known.