Expanding on SomeoneElse's store idea once more!
I feel like the addition of being able to buy, one, maybe two more carriages would be nice, or just to overall make the carriages bigger. I feel like it'd be nice to have it so you can fit more passengers and therefore get through Stations 20+ a bit easier.
I also want to expand a little bit more on that whole lustful status I brought up last suggestion. I feel like if you'd place two lustful characters next to eachother, they'd become a lot more clingy to one another, having their moods be decreased severely if separated, but rewarding more points than usual when next to eachother, it allows for more strategy during session and whatnot, thinking about which lustful passengers are worthy of pairing up during a Station. Also, when placed next to one another, lustful passenger's time could also change to be matching, the lustfulness making them drop everything for their new lover.
God, I'm writing paragraphs for suggestions about a game where you put fatasses into a subway.