Can you explain? As a cheap and pretty much failure-free means of visually broadcasting the identity of a vehicle, they seem pretty irreplaceable. Anything requiring electronics is much more prone to failure. Even airplanes have their call signs written clearly somewhere on their body.

I'm not sure on your logic for that statement, but I can't agree with it as presented.

Reporting of impaired or unsafe driving is something worth preserving, making that require technology severely limits the pool of citizens able to do that, and I don't see any other way to preserve it.

If I took off my license plate, that would be noticed quickly. If I were to disable my car's transponder, how long would it take for anybody to notice? Transponders would not be tamper evident at first glance and are therefore not, and never will be, an adequate replacement for license plates.

Yep, I can take plates off of relatively anycar I see, preferably the same make, model, and color. Skip tolls, red lights, kill anyone, be a get away vehicle, collect parking tickets practically do anything I want where I didn't want to be identified by my license plate. License plates unless they're permanently affixed to cars is a bit outdated.

Identifying license plates on the vehicle should be more permanent. Similar to the VIN. Otherwise if they can be changed so easily they're kind of pointless. They operate on good faith.

How else do I tell the hotel which car is mine?

Tell that to face recognition technology.