Hello BlackSix.
Have you thought that you should make the SDK available, and anyone can make a plane? Of course, this does not mean that crappy home-made aircraft would be included in the game: the full control, and integration into the game can only happen through 1C/MG? Like the DCS Mig-21, for example?
The publisher would be happy, because it saves work, but the game is developing.
The third-party developer would be happy, because after the sales he will get money (various percentage after the modeling, animating, texturing, programming). I think, it will be not problem, if we can buy these exras in the DLC system.
The players would be happy, because their needs will be met - even if they pay for it. Other aircraft, aircraft variants, ground units, ships, anything (I'm just guessing, if we get driveable land vehicles, the ships will soon. right?
).
The DLC system is no problem if the large maps, with base planeset is also available for purchase directly from 1C (important for online play, the basic game have to contain a basic, all-purpose planeset. Do not be a disadvantage, who does not spend fortunes on the extras).
The point is, everything need to allow by 1C. Too much user-freedom ruin the game balance. But it should be possible, that the community can able to help in this long and difficult task.