No chance for a 3rd cargo loader or, at least, not very likely, because it will cause more problems with routing between vehicles on the parking, and will require rechecking *all* starting positions for the additional vehicles for all sceneries and customized sceneries out there.
The most likely solution, would have one of the two existing cargo to go on the main door, but we'll need a new model, because the current one can't reach that high. If it could, we would already directed one of the two loaders on the main door.