I don’t think it will work at all. I think it would make the problem much worse, not better.
Think about that for a second: Police are never convicted, and rarely officially sanctioned. They always get away with it. Insurance will never pay out, so the cost of insuring officers will be next to nothing.
But, now we have an insurer with a vested interest in clearing the officer of wrongdoing, lest they be forced to pay a claim.