They are beautiful moving stills.
Some people say that adding these as loading screens would be more immersive, but unless there is a way to customize loading screens I’d have to disagree. Each of my saves looks and feels completely different to the shots shown in this video.
If I were to get a generic “travel between worlds” loading screen of a girl (or even my sim) sitting on a train, it might have the complete opposite effect and actually break the immersion. For example, my sims may or may not travel between worlds in very specific spaceships. Or by submarine. Or something else.
Unless I can see my spaceship travel through space, I don’t want to see anything but a blue loading screen. I’d rather close my eyes for a moment than be pulled out of the story by a beautiful cinematic shot that has no place in my sim’s world.