It's obviously possible techincaly (see cheap tablets), and from law POV (see seat belts requirement).
It would be useful (the device can have cheap black and white lcd screen and show "radar"-like view with cars ahead and behind).
It would also increase security even if there are no automated cars (overtaking tall cars will be much easier for one thing). Of course - if some cars don't use it - it's actaully decreasing security, so there needs to be adjustment period.
And when these things are in place - automated cars are much easier problem.
Pedestrians and cyclists would surely protest.