As a huge fan of the Transport Tycoon games I am eager to dive into Train Fever. I believe this game has so much potential. Please include cargo as a game-play element. This would truly take this game to the next level. I know this subject was discussed during your fundraising campaign but a solid yes or no would do wonders on this topic.
I see cargo being handled a couple different ways:
First a more simple way would be that industries produce something that needs to be shipped. The player is tasked with creating a profitable way of moving said cargo.
Second and more complex, would be that industries need employees to produce anything. The player is tasked with passenger routing that brings workers, which then allows the industry to produce the cargo. This would tie the passenger and cargo parts of the game together.
I doubt you want to create a full fledged economic simulation layer to the game. So having a smelter require coal and iron ore to produce X amount of steel to be shipped to, say a shipbuilding facility might be out of scope, but it would allow for a depth of game play that would exceed the hopes of Transport Tycoon fans.
I know first hand making a game is a huge endeavor, I myself am prototyping a city building game right now and know full well all the little complexities involved. So my hats off to you all for the effort and successful fundraising campaign!