That’s a good point. I’d expect immature industries to have lower production, so if you have a train with wait for full orders then it’s going to spend a heck of a lot of time sitting at a station burning maintenance costs.
One thing I haven’t seen yet is whether different industries have a return that’s based on speed of service like mail. If stations are strictly split between freight and passengers does that mean that there’s no mail like the TDD games?
It would also be interesting to know whether an industry has preferred destinations, e.g. does a coal mine only want to deliver to a local industry, or is it open to you opening up a long distance rail route to a consumer a long distance away?