It is time to start adding a few "twists" to the game to keep it from getting stagnant. Perhaps they could change by era. For example in era 1 we see a fledgling rail system. Breakdowns were common during those times and somehow could be incorporated into the game. We also saw a series of train robberies in the United States during the 1800's that live on in lore to this day. The Pinkerton's were formed due to the train robberies. So you could experience periodic loss of goods and revenue based on random robberies. A new station building could be created, the Pinkerton office. The higher your Pinkerton level the more you reduce your chance of having The Great Train Robbery of 1963!
Rail of course is an intricate part of a nation's logistics and economy. In fact rail companies can be public or private. Here in lies another twist to the game. You may chose to leave your company as a private company or you may chose to go public, issuing stock to raise funds for the game. Dividends could be issued, raised, or lowered and players could buy and sell their own stock or the stock of other players. Daily returns would be based every individual's daily performance. Extra cash could also be raised by issuing bonds with a chosen maturity date and an interest rate offered based on the credit standing of the player. Of course a new brokerage firm would need to be added to the station.
Elon Musk is working on mag tubes with his Hyperloop. Perhaps it is time for an era 7 to be added. For this era there should be 4-6 new goods randomly placed around the map with only one or two locations for each. These goods would only be deliverable to the top ten cities that would be in the end game, but locked by the end of era 6. Mag tubes would be the only form of transportation of these goods and the time for delivery would be fairly short. However, the top ten cities should have to use the same facility as the other end game cities due to the limited availability of these goods. Construction of the factory would start in era 5 with limitations on how high you are able to level the building in era 5, 6, and lastly 7. The factory would include two parts, one for the actual construction of the mag-tubes themselves, and the other for the research on the tubes.
Just a few ideas of what could be added, feel free to criticize, enhance, comment, or add more ideas...