The reason automakers include cellular radios already is to do app-to-vehicle and vehicle-to-internet communications. Things like Internet radio or unlocking your car from your phone need the Internet, and cellular providers offer that. Presumably at a cut-rate deal compared to general-purpose cell plans.

The spectrum in question was being held for short-range vehicle-to-vehicle communications (Wi-Fi range stuff, hence why this spectrum will be... used for Wi-Fi).

So they're probably going to have the cellular connection anyways. And technically, it's not impossible for them to still use Wi-Fi bands... they're just likely going to have to contend with some more interference. I think more than likely, vehicle-to-vehicle communication should only be an additional indicator, not something to be fully relied upon, since other cars can "lie" to yours.