I endorse the idea of an adaptive spoiler. But the main problem IMO remains unaddressed: how to mitigate the serious amount of energy that is released when a piece of road debris penetrates the underbelly of a Model S traveling at speed.
Any deflection or armor will hit the the debris. But only harder.
I suggest an aluminum honeycomb sponge between the front axle and the battery pack.
1. The spoiler will trigger the dangerous upward move of the piece of debris - instead of the battery pack
2. the piece will tilt upward and penetrate the soft honeycomb structure
3. the honeycomb structure absorbs the kinetic energy
4. the piece gets caught in the structure and is dragged along without causing more damage to the car
5. the honeycomb structure allows additional movement of the piece (e.g. driver slams the brakes, making the car nose down)
6. impact sensors signal the driver to pull over.
The honeycomb structure gets replaced in the shop. The piece of road debris can lead to the owner responsible for losing it, and insurance is approached for damage repair costs.