The LIMITED instant replay is solely for determining whether a ball was a homerun or not. It is not designed to judge balls and strikes, traps, etc.
It is designed to fix a highly visible and controversial area. The human element of balls and strikes, safe or out, none of that is effected, and frankly, with balls and strikes, would probably be technically impossible to do.
Great decision - will speed up the game, and make them more accurate.
R.I.P Tim Minnick
The KING of Cards