OK, just an off-hand thought, but...
What if they used a sensor-sock as more of a leg-covering on the leg above the ankle. Then the Addidas equipment could score any contact with enough force, but it could be programed to zero out and not score if the impact was with the wrong part of the leg. What'd'ya think? Personally, I would love to have some kind of equipment that could measure the force of hand techniques and punches, and score them regularly and uniformly (without some judges' personal bias against punches).
As quirky and problematic as it is right now, I think that some kind of standardized instantaneous electronic scoring system is inevitable. And frankly, if done right (so it actually measures impact force/power), it will be a great training aid and a benefit to many martial arts.