As an ego thing, what would be practical would be that you could have custom skins for your plane, so if you wanted to fly a hot-pink P-51 you could, but it would only be on your FE. Allowing people to fly their own custom paint jobs on their FE wouldn't affect the game, and it would allow for some interesting screenshot opportunities.
Another thing that would be interesting is to allow custom skins in the standalone movie player, so you could assign a skin to a particular aircraft. This would be useful for things like producing instructional films, where you could make high-visibility skins so the people playing the films can see clearly what all the planes are doing.