I just had a great idea for one of my fanfics.
The Tale of the Pony Express.
It's a story of how the railroad in equestria was made. It tells of a great colt who became prosperous with the railroad. It's a late 1800's theme, and kinda relates to how railroads expanded though the US. I guess since I'm sort of a train junkie, I could write this fan fic pretty easily.