Possible, just look at Forza.
Necessary? Nah. The more customized it is the more that has to be done to carry that online as well. I'd rather have the game.
I do hope that in MP it's possible to have different preset skins for fighters on each side, especially if we aren't required to be split as allies vs. axis, just to help with differentiation. That's all that's needed.
Otherwise, I'll be inside the cockpit, so the color of the tail of my own plane is irrelevant and painting them individually would be detrimental to the team. Remember, sim mode won't have any labels for friendlies.
