Could work in principle, but the sensor package would have to be inviolable, like the crash boxes on airliners.

The current system based on claims tells the true tale to the insurance companies, as far as they are concerned.

Or violable, and let that be offset by the honesty of the average joe, the criminality of getting caught with a modded one, and the difficulty of creating consistant data with a "comon sense" congruency. If you measure speed on three diferent spots, well you can see how tough it would be to fake... And should you run a programed transmision that contradicts the streetlight timing record well, you're caught.

Things are already done along this path

See: http://www.greenroadtech.com/insurance-programs/

it's just an advisor, it doesn't report with, say a blackberry oem...