I've been beating this drum for a while. In most sports the team can guarantee that their best player has a chance to score when the game is on the line. The Cavs can put the ball in LeBron's hands for the final shot, and the Patriots can call a pass play on 4th and goal so that Brady has a chance to win the game. But in baseball, you're stuck with the lineup. If the bottom of the order is up in the bottom of the ninth, you pinch hit and take your chances with a sub in the field.
I'd like to see a rule change where a team can bat anyone who has not yet been removed from the game once without losing either player. Imagine the bottom of the ninth, bases loaded, Yankees down by one, and up steps -- Ronald Torreyes. Maybe he started because Castro or Didi is a little banged up, or he pinch-ran for Headley earlier in the game. The Yankees could pinch hit with someone from the bench, but then they might have hole in the infield if the game is tied.
What if they could pinch hit Gary Sanchez? If Sanchez is on base, Torreyes has to take his spot and Sanchez hits. If he's not on base -- he made an out or scored earlier in the inning -- he just bats for Torreyes. Once his turn at bat is finished, Torreyes and Sanchez have to switch. If Sanchez walks, Torreyes goes to first. If the Yankees want to pinch run for Torreyes, they can do so and Torreyes is out.
This will give each team one last chance to put their best player in a position to win the game and inject more strategy. I might tweak the rule so that a player can't bat twice in a row -- if Sanchez just struck out, he can't get a second chance by pinch-hitting for Torreyes. I might also go for a similar rule for pitchers, but I feel like managers would just use that to get a LOOGY in for one batter, then go back to whoever started the inning.
I'd also like everyone to know that the whole time I wrote this post I was thinking of the "What are the rules?" song from the season opener of It's Always Sunny in Philadelphia.