Practically it would take several seasons for the rule change to settle in and for coaches to adapt their tactics. The game is all about winnng trophies nowadays and any team manager who lost an important game would blame it on the rule change . What incentive would a team like Manchester United have for supporting any change in the status quo?
I'm not sure if a rule change would speed the game up myself ,it might even have the opposite effect . I have (distant)memories of playing in the school playground without any off-side rule. There used to be a bunch of "goal-hangers" in the other teams half waiting to get the ball kicked up to them with markers from the opposing team trying to crowd them out .
Why was the rule first introduced?