Next will be Radar and cars that have no reverse gear.
Sonar, actually, and there are cars with "obstacle warning sensors" and you can identify them by seeing rear bumpers with little disks on them.
I don't know if I agree with making the back up cameras mandatory, but they should certainly be optional. But the problem with mandatory safety features is that only the safest drivers to begin with will order them. Plus, only by putting them in every car will the cost drop dramatically enough to bring the cost way down for the rest of the public.
I know that I've bumped into things behind me when they were too low to see over the trunk lid.
Mark