Hangar doors slid open to reveal a fleet of white Mercedes-Benz vehicles arrayed on a rain-slicked runway. As fireworks shot skyward, an imposing gray sedan zoomed forward onto a temporary stage, delivering Alicia Keys, in a dark floor-length evening gown, to the piano where she performed with a local backup band, the Hamburg Symphony. Befitting the flagship of the Mercedes line, the premiere of the new S-Class at a vast Airbus jetliner factory here on Wednesday night was a grandiose event. Always a showcase for luxury appointments, this latest incarnation of the S-Class is notable for much more than features like the so-called hot-stone massages offered by its reclining rear seats. Or the Wi-Fi. Or the cup holders that keep drinks warm or cold. The 2014 S-Class, which goes on sale in September at an estimated starting price of $100,000, is a significant advance in the development of autonomous autos.