Technically the continuously overwritten ring buffer seems hardly more difficult to implement.
One big problem would be battery life. There was a fatal police shooting recently which the police officers' cameras apparently did not record. One reason I heard was that they have 3-hour batteries which are supposed to last for a 12-hour shift. At the very least you have to keep a charger and spare battery in the patrol car to make continuous recording work. Better if you could actually make a single battery last the whole time and take away any plausible reason for not having a recording.