My understanding is North American railroads both promoted existing attractions and developed their own. Can you imagine how players would react if building rail on unimproved tiles rolled a chance of up to five tourism? It could be interesting to introduce some rail-national park tourism boost.
Containerization is a great idea, and the Container Terminal would make a great Tier 3 building in the current setup. I am unsure whether it would be better to have a late-game district or late-game infrastructure. It would be easier to achieve proximity of three districts than four. I am emboldened by Humankind to imagine a Train Station district, so perhaps the tiered infrastructure would be Passenger Service, Container Terminal, and High-Speed Rail. While I am district-happy, why not separate Commercial Hubs from a Financial District? The former could keep markets into a new shipping function, whereas the latter could have a Mint-Bank-Stock Exchange progression. I like the idea of containerization offering a bunch of multipliers and possibly incentivizing late-game district development to exploit them. Of course, if we had ports, train stations, commercial hubs, financial districts, and commercial airports, we would be in fairly desperate need of counterweight to all that trade income!
Given the huge footprint on the ground of railroad yards, passenger terminals, freight handling facilities, etc, a separate Railroad District would be easy to justify - more easily than some of the other Districts, in fact. I suggest that the 'buildings' in it could be:
Passenger Terminal - adds Gold, Tourism
Marshaling Yard - increases Production, Trade
Container Terminal - massively increases Trade, Gold, Production
High-Speed Rail's big expense comes from the precision required in the track itself. My understanding from construction in Germany in the 1990s was that a kilometer of High peed rail costed out at the same expense as a kilometer of mutli-lane Autobahn - both designed for 100+ kph travel. Instead of placing the change/upgrade in the Railroad District, then, it should be a massive investment in the rail lines between the cities. BUT that investment might pay off in, say, the ability to share population, production, and food between any cities so connected, essentially extending the 'city radius' to the length of the High Speed rail line.
Separating Commercial and Financial Districts is an interesting idea. Presumably, then, Commercial District would emphasize Trade, Financial Banking and direct Gold Supply. The problem I could see is that a separate Financial District only appears really in the Industrial Era when it became necessary to concentrate and exploit capital in huge amounts to construct things like Canals and Railroads, both Improvements that required as much capital investment as Wonders previously.
That means that a new division of Buildings between the two might be necessary. Tentatively:
Commercial Hub District:
Market - general Gold in city
Caravanserai - adds Trade Route, Gold from Trade Routes?
Bank - more Gold?
Investment Bank - easier building of structures in other Districts
Stock Exchange - easier building of Improvements, Wonders, more Gold generally
Central State Bank - allows Production to be pooled between cities?
Just thoughts based on historical antecedents, which the game does not have to follow . . .