Well, problem with that would be mainly that IL-2 doesn't really have very good wheel physics, so you wouldn't get very much traction and your tanks would be slipping and sliding every which way they wanted to. The AI-driven tanks and vehicles move along "paths" on the ground rather than having any powered wheels or steering or such.
Making a plane that looks like a car or a tank would be simple, but it wouldn't really behave anything like real wheeled or track-driven vehicles. I think some mod packs have a Jeep and a Kubelwagen, and driving them is a fairly exotic experience indeed...
What would be more interesting is having multi-crew ships using similar physics as the floatplanes that are already in-game. Sort of like the recent mod of Space Battleship Yamato, but with the vessels being confined to surface. You would get rocking with the waves, and you could even beach the ship. Not sure if it would be possible to make the ship sink...