"The Scarlet Letter" t #3
Yes, BUT !!
The difference is, this new Tennessee standard forces motorists to pick a side, and display it to the world. This leaves anyone displaying a license plate vulnerable to the anger & potential violence of those who made the opposite choice in license plate selection. It's a compulsory chip on the shoulder. The State is merely granting citizens the option to pick which shoulder.
"I assume that they are wanting to allow people to give voice to their religious/political beliefs" mm #5
Plausibly that's Tennessee's fig-leaf. But if that were the real reason, drivers wishing to declare a position could put a plastic Jesus on their dashboard, or hang a string of rosary beads from the rear-view mirror. And then there's the old reliable, the bumper-sticker. Nope! This one smells like Boston harbor at low tide.
"I was shocked to discover that the same number/letter combination could conceivably be issued in more than one state" mm #5
Totally.
I gather it took decades for the individual States to coordinate a "points system". Before that, a drunk driver, speeder, etc with many convictions in one State could drive unfettered in another State.
But indeed mm, you've identified a glaring example of the 10th Amendment in action.
B. O. R. ARTICLE #10: Ratified December 15, 1791
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Your suggestion mm is an excellent one of course. And now that license plate scanners are proliferating among police departments across the nation, it may become a necessity to implement your improvement. But bitter personal experience indicates, they'll delay that as long as possible, particularly if it's perceived as merely an inconvenience to citizens. Once revision is perceived by them as a benefit to them, progress will suddenly become imminent. Welcome to America.