Actually the Rhine River Cruise if it had been built as intended would be a strange document of cold war history by now - and would have been starting 8 years after the opening of EPCOT Center. It was supposed to showcase the rivers Rhine (Cologne, Düsseldorf), Tauber (Rothenburg), Ruhr ((Ruhr area, especially cities like Dortmund and Essen, the center of German heavy industry) and Isar (Munich) and was supposed to celebrate Germany's famous rivers. It was totally focused on West Germany at that time. I can't imagine a ride like this being built today leaving out the Spree which runs through Berlin.
But then it was a strange pick of rivers in the first place as it left out the Danube which at least has its source in Germany (unlike the Rhine which has neithre source nor its end in Germany, it just passes through) and the Elbe that flows out into the North Sea north of Hamburg.
However, I think it was a ride concept that was fitting for the original theme of the World Showcase and a "ride the Disney movie" ride never would fit. In the end it appears that there is no vision any longer of why there area different parks. I think they all need an identity that is visible to the visitor in order for having a reason to be around. Otherwise why build different parks in different locations on property if you put the same stuff in every single one of them. Just to make it more difficult to visitors to travel from one set of attractions to the next?
I also believe that a lot of these things like coherent theming might not be consciously noticed by the average guest, but it lays the foundation for their experience and creates what people might call the "Disney magic". By having a strong thematic base the experience itself becomes more than just going on fun rides. It is something intangible that most people don't notice until it is absent.
