I think you'd end up with the same problem we saw when using a single model with a selection of skins - the ETO Hurricane does this, for example. The problem is that all AI Hurricanes spawned during that mission will use the same skins, and we wanted to avoid any possibility of that happening. Ideally each AI spawned is going to be a different aircraft type, so if you have 10 different AI Spitfires, say, you should get 1/10 probability each time. It's more fun admittedly with German aircraft, where the skins are more diverse. I see though that MS has done precisely that with the Ju88 though...
It does seem a bit unnecessary just to gain a bit of storage.