I knew this issue would come up.
There is already case law on this in GA. Officers do not need any reason to observe your license plate and run a query of said plate on GCIC/NCIC. A license plate is property of the state and your registration information is already on file with the state so its not private to begin with. As long as the officer is in a place where he is legally allowed to be he can view your plate and query it.
A license plate scanner just does this same thing for the officer automatically, and it doesn't even reveal your information to the officer unless your wanted, stolen car, no insurance, amber alert, etc.
When I was in uniform patrol I used to run hundreds of tags by manual entry a shift looking for stolen cars and wanted people. Almost never came up empty. I could care less about tickets, I wanted the career criminals. This device helps officers do the same thing.