One thing that I'm not sure that has been discussed is the Windows on the train. The windows are not just LCD's that your looking at. Think of it more like a window, with a Harry Potter Forbidden Journey Dome Screen against it. You will be able to move your head around by the window and see different angles of this 4k image on the dome screen.
Here is a description of it from
http://www.mugglenet.com/app/news/show/7856
"The Hogwarts Express journey will not be like anything created before at Universal. When asked if it compared to the King Kong Experience, DoQui replied, "No. This is very unique technology. Imagine looking out a window and being able to look to the edges of the window, up and down, and get all of that story information. This is unique to each cabin - they're getting the same journey and story experience but from the point of view of looking out the actual window and getting that actual detail.”
Now if you look at this image, you will see how the left side of the train sticks out with a curve to it. This is for the mini domes for the windows that you will look out.