Are they going to take the Amazon Kindle route? Pay one price for the car or pay a lower price for the car that shows you ads? Not that the car makers would use it to lower the price of the cars, but raise the price of ad-free cars I’m sure.
At best you'll get some sort of nearly worthless concession because they have to slap in cellular hardware to make the ad bit work - something like you'll get free traffic updates on your gps nav (sold seperately) - since they need some sort of enticement.
No way they'd offer anything remotely looking like a meaningful discount.