> We still have the problem of what to do when the reading is invalid on multiple sensors.
Mechanically would it be possible to have 2 on a turntable, one always inside (warmer) and if the hot wire on the outer one indicated a block, the turntable rotates the outer one in. I realize this is a mechanical mess and adds all the unfavorables (cost/weight/complexity) but if it could be done, it would certainly get you a fresh ice free pitot for a little bit.