How is this "sharing?" This seems like app-based short term rentals little different from what I could get from Avis and the like. My initial thought was that this was allowing individuals to rent out their cars and my reaction was a hard 'oh hell no.' What's the term from the various "my expensive camera /lens was stolen" stories? Voluntary parting? Pretty sure that would apply to your nice car as well.
Presumably there's an implied distinction between this model, where people share ownership of their primary car, and the typical rental car model, where people are presumed to be traveling or otherwise renting the car to supplement their existing car ownership.
Not saying it's some brilliant insight, but there is an internal logic to the use of the term.