New Fords, Volvos and Vauxhalls with drivers assistance packs already have forward facing cameras to spot speed limit signs and obstructions (such as pedestrians) in front of the car. A great many cars have rear facing cameras. Some Range Rovers have surround cameras, and Nissan recently announced this feature on a special Qashqai model. So it would be possible as part of an accessory pack if there was sufficient demand. I suspect there already is in China and Russia, where most YouTube dashcam footage comes from. This footage is not evidential in itself, but if it fulfilled certain criteria it could be admitted as evidence.