If we're going by the "plain view doctrine", you can cover up any item in your car with e.g. a blanket, and an officer would not legally be able to move the blanket to see what's underneath without a warrant, probable cause to search, or permission from the vehicle owner (I'd add the caveat that seeing the shape of a gun underneath a blanket could probably pass for probable cause).
So, moving that boundary from "the blanket" to "the window" to me seems pretty reasonable, except that a window tint doesn't completely obscure what's behind it like a blanket would. A tinted window fundamentally can't protect from plain view in the same way that non-transparent object can; the owner would be better off hanging curtains from inside the car.
Or a Sony analog IR-peering camera that had an un/fortunate feature of looking through clothing. Is it "plain view" if using a camera that can see differently than humans can?
So, moving that boundary from "the blanket" to "the window" to me seems pretty reasonable, except that a window tint doesn't completely obscure what's behind it like a blanket would. A tinted window fundamentally can't protect from plain view in the same way that non-transparent object can; the owner would be better off hanging curtains from inside the car.