Imagine a world in which hardly anyone owns a car. Instead, most people subscribe to a service for self-driving cars, probably a mashup of the current players in the space, which include Google, Uber, Lyft, Apple, Chrysler, Volkswagen, Tesla, BMW, Toyota, General Motors, Ford and others.

Call this hypothetical service Applewagen, or Tyft or, what the heck, Goober. The service is great. You whip out your circa-2025 smartwatch, which has all but replaced your phone, bark a command and a self-driving car appears, from a fleet...