Maybe a solution would be to have a "bank" of bags like duffel, some boxes, strollers etc. and then have the engine randomly pick some? So like what they do with the caterers or servicemen? I don't know if it's possible, but just a thought.
If it was that easy, we would have already done it, long ago...the issue is, the baggage animation is very tricky and complex, and is tied to the man handling it, and is also synchronized with the baggage train, since a bag start its life as hierarchically linked to the conveyor belt bone, then it's passed in the hands of the man that picks it up, then it's passed to the wagon.
In fact, with the container pallets, we made it more flexible, but it was easier, since nobody has to touch the pallet, so it can be a separate objects that can move on its own, and thus having multiple liveries easily.
As I've said, we might have two different colors fairly easily, but not many variations at the same time.