Well, I've fixed it (it was actually one missing material node), but unfortunately, I was unable to improve upon the King Air, since MSFS does not provide a variable to access the amount of windshield icing. This means you will get some mildly strange behavior if you run the windshield wipers while the glass is iced over. No different than the King Air, though.
As usual, I did find something to improve, though. Here is a preview from the changelog:
Windshield wipers now flutter when deployed at high indicated airspeeds, and also become jammed when airframe icing is moderate.
When the wipers are deployed at high airspeed, the apparent wind will affect the resistance on the motor, slowing down the downward sweep. At high enough wind speeds, the wipers will not return to their parked position at lower wiper speeds.
This was a particularly fun effect to program, so I hope you enjoy it!