This improvement will feel quite massive because it focuses on the AI passengers on the routes. The core feature would enable the passengers to be more dynamic and give you feedback on how you drove by screaming and panicking, or feeling good or worried about your speed, you could interact with them on the platform. You would hear them talking as they climb onboard or on station platform or even during the trip or as they are exiting the carriage. Maybe you could introduce pram with baby on board, people with disability and wheelchair access which will delay your trip a bit.
I am kind of envisaging SIMs like smiley or frowny faces above passengers heads as they wander off though
Think even if this feature was wanted by consumers. The UE engine currently in use only supports a limited number of channels. Theres already a case for reducing ambient sounds on routes, so to make sure that the real focus of the game (trains) can be heard appropriately and at their best levels. For me personally, Id ditch most ambient sounds (reintroduce them with a future UE4 upgrade) if it meant I could hear an oncoming train from farther away(as they should) or to get a PA announcement at a station as a train approaches.
You mean you haven't already? The guy in the grey raincoat on NTP I call Johnny Marr as he looks like the Smiths Gutarist!