For the most part, car door technology hasn’t changed all that much since the first cars were designed. Consisting of two hinges and a latch, car doors open outwards. There’s nothing really wrong with this design and that’s probably why it’s been in use for so long. However, if there are opportunities to improve upon the design, why not?
Rather then opening outward, in the Disappearing Car Door concept, the door drops downward into a pocket on the underside of the car. Some of the advantages of this technology include fewer dings on the door, more space for those with special needs and the fact that you cannot be “parked in” by another car that is parked to close. Of course, you can’t forget the coolness of this technology. As for practicality, I’m still undecided.

The idea of a door that folds down beneath the car is interesting, but what if you live in an area where salt is the road solution for all weather conditions — what happens when your exhaust pipe rusts out and is dangling beneath the car, and the door hits it? What if the battery dies — how do you get into the car so you can open the hood to jump-start it? What exactly does this cost? Carmakers go to great lengths to limit the cost of producing their products. For your swing-down door, I’m thinking you’d need a pretty heavy-duty motor and complex linkage, lots of steel to strengthen it (since the B-pillar is gone), and lots of time and labor to ensure it’s aligned correctly. Like I said before the jury is still out on this one.
Take a look at the video which further details the Retractable Car Door.

Disappearing Car Door

Disappearing Automatic Car Door