Utilization levels will be driven by peak demand, as the usage patterns are highly nonuniform so I don't think they'll be that different. Also remember that even during peak hours, cars will be traveling between fares, potentially half the time (since demand is often mismatched during peak hours). Because most of the costs scale per mile, I don't think the immense cost savings will materialize.

Now robobuses is an idea I can get behind, since labor costs do dominate there.