I've mentioned this before on another thread but I thought of a brand new district, a Tourist Resort. The first building would be a railroad station and from there you could set a path for your freight trains to connect to another city with another railroad station and it acts like a domestic trade route. Later on those same routes could be used for tourism purposes and can turn into passenger trains.In the case of railroads, their exclusion from the game immediately made me think of all the Real History effects of railroads: increased productivity and a quantum leap in communications, leading to increased mobility of populations (mass tourism), massive increase in size of armies (increased supplies) and massive growth of cities (food supply no longer dependent on nearby sources or water-borne transportation). And, sure enough, NONE of those things are in the game either, making the late game (post-railroad) Eras merely a More Of The Same experience rather than a Revolution in Human Affairs represented by the industrial/railroad revolution...
A hotel can then be built in that district and a choice of another third tier building: Theme Park (tourism and amenities), Casino (tourism and gold) etc.