I strongly agree on point 4, adding more goods types for cities. Where a city would really start growing when all the goods types are being delivered. As it is now, you can just hit each city with one goods train and it is done. Having to deliver different kinds of goods for each city will challenge the player to build more complex traffic which in the end is the best fun in this game. Also could add more dynamics into the gameplay as the time moves forward, changing the demand of different kinds of goods across different eras would demand the player to change or remove existing routes and build new ones. For example increasing the demand of oil after the population starts using own cars, etc.
Also the idea of prolonging the 20 minutes rule for cargo is very attractive as it would make more complicated cargo delivery models viable, like moving cargo from close factories together to one central hub and then delivering it with long trains across the map. It is possible now, but sometimes limited.