At that point, it's less of a parking structure and more of an automated valet service. You get out of your car and only your car enters.
Taken to the limit of the idea, the whole parking structure could be entirely sealed to the outside, and maybe even evacuated or filled with a non-oxygenated medium (e.g. nitrogen) to prevent car fires and reduce rusting from long-term storage. Sort of like a modern grain silo.
My line of thought started from, "what would the world be like if every vehicle had a built-in valet?" I think the design of commercial areas would change dramatically within a couple decades, even just from the effect on parking.
Taken to the limit of the idea, the whole parking structure could be entirely sealed to the outside, and maybe even evacuated or filled with a non-oxygenated medium (e.g. nitrogen) to prevent car fires and reduce rusting from long-term storage. Sort of like a modern grain silo.