I think you start with speeding up time between innings/pitches, not with penalties that affect the actual game but maybe with a fine system put in place (taking too long on the mound or stepping out of the box too long/too often, so it affects everyone). One mound visit per inning...any pitching changes or anything past that have to be called in from the dugout. There is no reason replays should ever take more than 60 seconds. Get a dedicated team at headquarters and have them in charge of everything. Those seems like much more reasonable ideas that have zero impact on the actual game play. If there isn't any noticeable difference in time of game (which I think drives 'interest'), maybe then you consider more drastic measures...limited pitching changes per inning, altering the mound/strike zone, etc.