I could see the camera mounted inside the rear glass in a small cover where the rear wiper cleans the glass. Simple design challenge however the bigger point is the current design is no better or worse than any others.
To be honest, in bad weather while the clarity changes it hasn't been an issue for me. Wonder what snow and slush does with the sensor for driverless cars?
To be fair my C220 coupe had it's camera exposed from behind the badge which would flip up when in reverse. I still had issues with water drops and smearing. I think a hard thing to get around no matter where or how it's located
I keep a bunch of old bar mops (towels) in the bin on the right in the cargo area to wipe down the camera and wipe the black crap off my tail pipes. I’ve just gotten in the habit of wiping down the camera before backing out in the rain.