I think it would be more realistic if certain types of freight cars can only carry certain types of freight
i.e. Open hoppers can only accept stone, gravel, ores and solid fuels
Gondolas can handle almost anything except tools, weapons, seeds and crops
Flat cars can only accept, logs, wood/wood products, stone, iron/steel and associated products (blocks, scaffolding, etc.)
Covered hoppers can only accept seeds, crops and other bulk items.
And the list goes on.

I could have swore I had a ticket for this, but I guess this can be the ticket to track the work for 2.0