They do, but, I do own my car. I pay ridiculous amounts in taxes for said roads. I also pay registration as another tax. They can do to the plate what they want, but so can I as an act of Free Speech.
These things are going to consume some power... is the government going to lower taxes on fuel to compensate for the amount of fuel it takes to power these license plates?
Maybe they will be battery operated... what happens when the battery dies? I will say what others have said, if I wanted to drive around a billboard for others, I'll choose who I advertise for.
You know as well as I do, the day these are foisted on people, they will be hacked. That is more of my tax money wasted. I really think that is the crux of the issue, it is nothing more than a flagrant waste of tax money on something that is going to end up costing more in the future than it is worth.