“In recent years, as artificial intelligence has advanced, Flock has added the ability to search for cars based on their make, type, color, or unique details, such as bumper stickers or visible damage.” So TOTP license plates is not enough.
IRL we will probably need more mature solutions - legislation, regulation etc. At this point we know the tech can't really be contained. It'll be all-seeing, all-knowing and super cheap. Just as the source/link describes it. So the only way is to have actual adults working in law enforcement.
Also the cops would just get the private keys from the DMV anyway. It's all the same government.
I don't think that's been the case since 9/11. It's naive to assume the CIA, FBI and NSA don't have root access to every device and every account in existence, or couldn't get it if they wanted it, legally or otherwise. I don't think your local DMV is going to be the hard line keeping the feds from knocking at your door.