The short answer is that your point is well taken. I have no idea what the volume of violence currently on television would require in terms of that kind of advance screening. It might be that, practically speaking, you would have to develop a system by which a broadcaster submitted one episode of a series, or, if a broadcaster had not received any complaints over a period of time, they would be released from the responsibility of doing that.
I've come up with something that I could tell you in ten minutes, but if it were genuinely something that there was interest in implementing, I suspect that there would have to be a more sophisticated mechanism to develop it.