It'd be great if there was a mod for making this like OpenTTD :-) I.e. have existing towns/cities that AI grows organically while you build a transport company.
What's always bugged me about Transport Tycoon is that passengers just want to go somewhere. It'd be great if passengers wanted to go to specific places. There's loads of scope for a proper simulation to add more depth to that sort of game.
A-Train (which also works like that) was a huge inspiration for me. All that's missing would be a way to auto-grow all other infrastructure except the transport company's. Then the rest of the detailed simulation should already "just work".
What's always bugged me about Transport Tycoon is that passengers just want to go somewhere. It'd be great if passengers wanted to go to specific places. There's loads of scope for a proper simulation to add more depth to that sort of game.