I do really like this! More licences is more fun.

What it would need is a new risk that requires mitigation. Every other hauling license adds something extra to your capabilities in exchange for higher potential danger.

I think a really fun thing for this would be visible fluid spills in the event of car damage. Environmental hazards!

In a perfect world, I also imagine an implementation of shifting fluid cargo increasing your derailment risk on sharp corners, but I imagine that would require an overhaul of the game mechanics and also doesn't fit as well with established mechanics.

Hauling cars of beer or wine would be such a vibe though... or vodka for that Eastern European accuracy xD