Imagine, if you will, an alternate 1973. A world like ours, but with one exception: Volkswagen selected this sliding-door Golf for production instead of the conventional, swing-out-door one. How would that world then differ, from the cascading effects of this one decision?
Conservatively speaking, I think we can safely assume that that would would have become an absolute utopia, free from war or want or pain. This prototype was developed, according to this source, by VW door and hinge supplier Lunke & Son. The benefits of a sliding door on a car like this are huge — total access to the open door area, minimal issues with entry room in tight parking spaces, and a different way to crush fingers in a closing car door.
I'm always surprised useful, convenient sliding doors haven't been more popular on small cars, and I think it's easy to see how humanity, freed from the tyranny parking lot-door dings and awkward entries and exits, would rapidly step up to fulfill our maximum, ideal potential.
Just like humanity did when Peugeot introduced the 1007.