I would love this.
To have the option to create and use liveries and/or stickers. On the plains like in Forza.
This is also a way to get IRL Companies Liveries/logos without having to pay license fees, du to them being free and user created. In other words, no one is making money on them.
I do hope this will be a IN game/sim feature and not a 3-rd party thing, cause that will not be friendly for the xbox players/simmers.