Ice protection would be easy enough to implement using the current rain delay. It would be fair to assume no one would set a 255 hour delay so have the weather script send a delay of 255 if current temp is less than 33f or predicted to be less than 40. Then have the controller turn off all programs until the rain delay goes back to something less than 255. On the controller it would be easy enough to log a 255 hour delay as frost protection.
Properly set up sprinklers should drain enough water to prevent frozen pipe breakage, for short duration freezing. Owners should be shutting their system down before major freeze events in winter. On a side note grass should not be watered in temps less than 45 F anyway, it prevents the grass from properly going into dormancy, and wastes water.