I looked at the data and the biggest issue I see with the 3 batter rule is that it won’t really make a huge difference: LOOGYs are becoming unfashionable, and the real issue is teams sending out their starter for 5 innings and then using relievers for an inning apiece from then on out, every single game. 538 noted that the correlation between relief pitcher use and K rate is really high and their solution, while a lot more radical, makes a lot of sense as well:
https://fivethirtyeight.com/features...lan-to-fix-it/
The biggest issue I see is how to prevent teams from just using a “shadow roster” of an extra 3-4 relief pitchers that they just shuttle in whenever they want to. The current roster rules make it so you have to burn option years to do this, but I wonder if it would be enough. Otherwise, this should at least impact the single biggest issue with the game, the high K rates, at least to some extent without forcing bigger changes (lowering the mound or increasing the size of the baseball while making it wound slightly looser).