The battery in the average fob can last years.

The battery in some people's smartphones can't even last them all day (because of their usage patterns and not wanting to carry a "brick").

I can't wait for all the stupid reports of "I can't start my car because I forgot to charge my phone and the battery died" once they go down this silly route.

Non-rental cars could use biometrics as long the drivers are consistent. But that wouldn't work for rental cars either.

Plus there are still some people who don't use smartphones (or at least don't carry them all the time). Are they not supposed to buy cars any more? I thus don't see is as the only starting option. It's one thing to have the option to configure your car to start via smartphone only, it's quite another to design a car to roll off the lot with smartphone as the only starting option. How do you test drive such a car??? How does the smog check person (in states where smog checks are required) start the car? How does a valet start the car?

Btw, the article you linked about Volvo makes it sound like they're doing this to try to lock on independent repair shops. They sound like they're trying to make Volvo dealers the only ones who can service you car, because they're the only ones who can start it (without your phone). But again, that doesn't explain what smog checkers do, what valets do, etc.