Why make it centralized? I generally am suspicious of "anonymized" datasets (in the abstract) as any usable data is probably enough to nonymize someone given a couple other pieces of data. Forgive me if you didn't mean a centralized system but I took upload and anonymize to suggest that.

In the case of cars some radio comms (uhf, wifi, or even bluetooth?) is probably sufficient since there is no reason for a car in New York cares about the opinions of a car in San Francisco. You'd probably even see performance gains under a distributed system since latency is effectively taken out of the equation (time of flight for local radio being effectively instantaneous).