The problem with this idea is that it conflicts with the rule on what is/isn't out of bounds. Unlike American Football, where the player's body determines if the ball is in or out-of-bounds, the rule in soccer is based on the location of the ball, and for ALL situations, including goals, the definition is based on the entire ball being over the vertical plane of the entire touch line or end-line.
IN fact, a goal can be defined as a ball that goes out-of-bounds between the two goal posts and below the crossbar.
To change the rule so a goal is scored if ANY part of the ball is over the goal line would make it inconsistent with the rest of the rules, or in the alternative would result in making more balls on the sidelines out of bounds, effectively "narrowing" the field and making it easier for the defense to clog up the game, making it even harder to score.
I will parenthetically add that the beauty of soccer lies in part with the fact that it doesn't take a 12 volume set of rules to make it work. Contrast that with baseball or American Football......