Seriously. Why not let pitchers come back? Think they’d be more likely to get injured? I think the opposite: Pitch a little, take a rest, pitch some more. Sounds like less wear and tear to me. Would also increase strategy talk that fans both love and hate. OK, impose some limits. Baseball is too slow. Can’t substitute every other batter. So you can’t come back in the same inning or even in the next. But alternate — one guy pitches the odd innnings, another pitches the even ones — why not? Get more out of these millionaires. Keep the rally-feeders in the pen. 

An earlier serious pitching idea posted here: Overhaul Baseball’s Current Rotation Setup. Of course, some rule proposals go way too far, like these from halfbakery.com: Batters Run Either Way (though, actually, this might increase chances of reaching base), Bat Use Change (Ouch! Felony on the field!) and Baseball Fan Interference Protector (You will sit down … NOW!)