Using your own logic, why couldn't an autonomous vehicle be a personal computer? The basic function of would be transportation, but what it would do better is integration with other Apple products and computing while on the move. I just don't see transportation and personal computing as being mutually exclusive.
But I don't think Apple's industry focus will ever shift.
Rather their/our definition of what 'personal computing' means will continue to evolve as the technology does.
An iPhone is a personal computer. An Apple Watch wants to be a personal computer. Apple won't ever stop being a personal computer company.
It's just that some day, a personal computer will be precisely that: a computer inside a person, integrated as software and hardware. A human iOS.
Surely that is the ultimate endgoal, and not an aluminum car (with a charge point under its chasis) that can talk.