I wonder if driverless cars could start out as a tool for people with disabilities. If such use were challenged, I can imagine the supreme court taking seriously a case by a person who is quadriplegic or blind demanding the right to use a self-driving car. If they can prove them safer, it will be hard to find a compelling government interest that could offset denying the use of this assistive technology.
They appear to be starting as 'driver aids' on new cars. Today's higher-end cars have adopted technology that alerts you when you drift out of your lane, watches your blind spots, safely follows the car in front of you, performs emergency stops, parallel parks itself, and adjusts vehicle dynamics in a multitude of ways.
My assumption is that this is a first step towards driverless cars, as it provides the manufacturers a way to test critical technologies in a safe environment. If the dealerships aren't downloading data from these systems, and sharing it back to the engineering groups, thats an enormous wasted opportunity.
I believe your assumption is correct as well. All of these 'new high tech safety toys' are the tip of the iceberg. With all of these components being used and people becoming comfortable with them, we will soon see more adoption towards driverless cars.
I think another major milestone towards this will be the next generation of GPS, with the increased accuracy it will help guide the cars where they need to go.
