I would love one of the empty number key binding slots to be where your still in control of the train, but you can be sitting in the passenger compartment sitting down, that would add to the realism, i like to pretend im a passenger as some stages through the game when im drving the train especially when im pulling up to station and departing them i dont like how i have to leave my seat then walk to a avalible seat and then sit down not knowing if im going over the speed limit or that i might come up to a red light... like how you can free roam in the fly camera view but still see all the tachometre ie Speed, Brakes, and power
On most trains use the '3' camera to go inside the train before you close the doors, you'll be inside the carriage while still driving the train. Although if you move the camera too much it'll glitch outside
I have a vague recollection, although it might just have been a beautiful dream, that in the original MSTS there was a passenger view like this.
And when there was more than just one coach with passenger view (or multiple views on the same coach), you could navigate using CTRL + 5... Key 4 ! Used in conjunction with 8, that was great and helpful for some nice screenshots... So there's still room for improvement in TSW !