What is going to make this fun for you?

[klem]

I think most of that is already possible with the FMB and scripting.

SEOW (attrition etc). I believe scripting can do this but I'm not certain.

Racing. Well, we have radar towers, airfield tower and Barrage Balloons to fly around.

Capture the Flag. You can set circular areas in FMB and detect with scripting when they are entered, put one around a hangar or an airfield.

Trick Flying. Don't know.

King of the Castle. You can spawn a/c at different distances and locations to arrive at different times, if you don't keep on top of them they'll get on top of you. You can also do 'last man standing' on-line.

Accuracy bombing. Don't know if CoD supports a 'target' but you could create one with rings of objects and script their values.