It will never happen.
FACT: Pitchers batting averages have gone down each and every decade since 1900. Be assured this trend will continue.
FACT: The only league WITHOUT the DH rule in the USA is the National League. Little League, High School, College and the lower minor leagues all use the DH rule exclusively. The AA and AAA leagues allow the NL affiliates to use their pitchers-as-hitters only in games between each other.
FACT: Although the pitcher is often the best ballplayer (and hitter) on his high school or college squad, from the moment he signs as a pitcher, he knows pitching will be his job -- what he gets paid for. Consequently, he's not going to waste a lot o his time working on his hitting -- which will naturally atrophy over time. And, quite naturally, his team has no problem with this decision. Indeed, most will encourage it -- because turning a young pitcher into a better pitcher is easier to do than turning him into a better hitter.
FACT: the lower your expectations the worse your results. If the MLB owners and managers turned to the pitchers and said: there’s simply no excuse for you guys to suck at hitting, learn it or you’re out. Baseball has decided they’re OK with pitchers being pathetic at half the game, and so they are.
FACT: The only league WITHOUT the DH rule in the USA is the National League. Little League, High School, College and the lower minor leagues all use the DH rule exclusively.
Gee, I wonder why pitchers' batting averages have gone down every decade?
Might it be that, because of all the DH's, pitchers don't take much batting practice?
Looks like a vicious cycle to me...