Double Height Train Cars

Double-stack rail transport is primarily limited for packaged items - anything that can be put into a standard container. While this may be an interesting game alteration (Double height trains only for packaged goods/double height flatbed wagons) I feel like extending the double height to hoppers would be beneficial as well.
Sadly, due to the rounded shape of tankers, double height tankers would probably end up looking comically oversized, but these could be addressed with the addition of heavier draw or high-traction engines, that facilitate higher speed for these tanker trains.
I only suggest this as, currently, trains sit in a spot that can make them difficult to justify compared to simply building out belts. With larger wagons, these could seek to compete more aggressively with belts.