It is a very old technology, back in 1980’s, BMW Z1. This Youtube video also uploaded in 2007, and the video looks very old. But, why this kind of door is not famous? Why other luxury car, Continental, Mercedes, Audi, Lincoln did not use this technology. It looks really elegant when the door disappear instead of moving around. And it is not just for style, but it is also effective and useful, for parking for example. And when the door is disappeared, the car look more spacious.
The doors retract vertically down into the car’s body instead of swinging outward or upward. The inspiration for these doors came from more traditional roadsters which often feature removable metal or cloth doors. Because removable doors did not fit within BMW’s design goals, the retractable doors were installed instead. Wikipedia