The problem with only using lenticular 3D is that it doesn't account for shifting perspectives.
I think that they will be using layers of transparent OLED screens on which varying distances of scenery will be displayed (mountains, trees, buildings, foreground elements, etc). Here is a demonstration of just how magical clear OLED screens are. Note, that the window in the video is clear glass, and the buildings beyond it are simply a painted background beyond the glass. All of the 'vine' effects that appear spontaneously on the screen are completely opaque.
I think this is highly unlikely. For one, The train is being constructed to actual scale with an interior and an exterior. There is simply no place for multiply layers of screen. Secondly, Although it creates a sense of depth, this is entirely dependant on the distance between each layer, therefore the effect would only work if each layer was mountains apart. In the end, with distant scenery there is very little perspective change beyond the "window", so as long as the eye tracking is used (in theory) and the screen's visual's have a constant forward motion, coupled with people buckled in their seats, restrained, there will be no need to ajust for the angle of vision.
Don't worry, I thought of that too back when it was rumered a screen tunnel would be used, and it's the technique used in old films and animation, in matte painting, to create depth. Unfortunately, it's disfunction off the silver screen is born very reason you think it will work, the 3rd dimension.
OLED is cool, but we don't want the exterior of UO showing! Unless of course, it could be used to make the windows look normal when the ride begins. On the other hand, This could be the way which we will see the "Dementor" attack behind the glass cabin doors in the train car, in addition to the frosting effect on it's glass seen in their presence. Though the OLED seems to work best with the color black.
PS: The OLED video adds proof to my point about perspective being unnecessary for the lenticular windows. If you watch the real city behind the OLED, despite the camera panning and dollying, the perspective does not seem to vary in an obvious way. This is a principle that will benifit the ride. In addition, the train's movie will be faster than the viewers head motion, therefore the lacking perspective will become indiscernible anyway and the illusionary depth perception will take priority.