It will never happen. The league can't put a cap on pitching changes without at least expanding rosters to 26 or 27 players. Sometimes relievers come in and just don't have it, look at Cecil yesterday. So if Cecil wasn't allowed to be replaced, would he just have to continue getting rocked while piling up his pitch count? He would eventually in that case be serving up 80 mph meatballs due to fatigue. The integrity of the game would be pissed on.