Sure, but data that doesn't flow back isn't much use to anyone, nor much of a danger to the consumer, and no amount of compression is going to make 25GB of raw

Sure, but data that doesn't flow back isn't much use to anyone, nor much of a danger to the consumer, and no amount of compression is going to make 25GB of raw data per hour per car for 100M cars anything other than very, very expensive. They probably send very little data.