I haven't seen it discussed much, but my guess is MLS prefers the finals to be in soccer specific venues. If the league is able to achieve the goal of building one soccer stadium per year, I think it will be a while before the Cup is held somewhere that it could break the record. And even if it is held in an NFL stadium, I think you would still need the home team to be in the title game to have a shot at breaking this record. Perhaps if they awarded MLS Cup 2004 to Chicago at the new Soldier Field, and the Fire made it. Other than that, I think the record is quite safe.