I remember seeing some stuff like this on the PC IL-2 forums, and isn't there a way you can "cartoon-ify" images with a lot of the more decent art programs? It would be a shame to lose the awesomeness of the BoP graphics, but it could also look quite cool if done correctly.
You could try to posterize it with Photoshop.. but cartooning basically means removing details . It'd both work out if done correctly.