While such a rule might sound good to you in theory, it's just not practical. Is it really easier to judge weather a foot or something else is over a spot on the ground at the exact time of release, than judging if is touching the ground behind the mark? When are you allowed to move past the mark after release? What about the run op on a fairway drive? How do you judge if the throwes is on the line of play on the last step before the follow through? If your follow through foot doesn't land right behind the mark, can't you just put your hand down there? Or your knee?
While your rule might fix one "problem" I think it creates many more and worse problems. And still no one offers an explanation why this is such a huge problem that it needs fixing?