[2015LXFIT]

Hi, this is an excellent idea however, I think it would be best fit with 2 side airfoils as well. I was considering engineering one for my 2015 Fit.

I think the proper way of doing it would be to have a voltage in split off of the brake light activation (not to be confused with running lights) to an arduino that has 2 limit switches.
In scenario A: The brake pedal is not applied, the servo has a feedback from the lower limit switch telling the Arduino that it is in normal position, no voltage is applied to signal in (from brake light).
Scenario B: Brake pedal is depressed, signal goes to Arduino unit, sending a signal to the servo(s), tilting your air foil, then hits another limit switch to stop sending voltage so as to not burn or break anything on the servo itself.
Scenario C: Brake pedal is released, and Arduino senses this, which switch is activated, and sends a power to reverse motor for airfoil down position, creating a loop so to speak in a programming sense.

The hardest part would be the programming IMO. AI may be able to do it but I'd definitely be interested in how this came about. I will say personally that I don't think just a rear spoiler would be enough. Ideally there would also be 2 side airfoils that pop out as well, perhaps in doors, or near the rear of the car, only popping out enough to make a difference without causing a danger to cars around, but should give you enough area to displace a second spoilers worth of volume, thus increasing drag. Additionally side airfoils could be eventually mapped in the framework of the vehicle to help with cornering and what not, but that's more for racing applications and you get into more finite engineering at that point.