As has been written many times, steam trains are not allowed in NYC. I seem to recall this rule actually still being on the books. I think of this every time I ride the Metro North into NYC.
I also think the mail car is one of those really good ideas that still is completely viable. So much mail moves by truck across the country. I'd love to see trains used (again) for mail. It just seems like such a smart way to move parcels around the country. I just got to thinking this the other day when I was taking some shots of this Ives Mail car (sad, probably).