1) This has already been created with Gwinda’s cargo mod, which is a 12 step chain, although it does end in goods. I suppose it would be nice to have towns demand food, or cars, but that would quite an extensive modification to work out the demands. How the city demands goods pretty complcated already.
2) I agree there could be a few more trains throughout history, but hopefully mods will sort that out. I imagine there will be DLC incoming which could be disapointting. I would like to see a few more trains to the vanilla game.
3) I don’t want shipping, or planes. This is train fever!
4) Definitely. Just a dropdown would do, can’t think that would be too tricky to implement.
A lot of your points aren’t really points for mods, more for the devs to implement to the game currently.