I want to avoid everything being automated and based on a measuring system that, quite frankly, could be manipulated at some point by teams/players in terms of high and low strikes.
I've long not wanted a full ABS system in place to avoid reviews on whether or not the seam of a ball grazing the outer edge of the black of the plate should be considered a strike or a ball in the 3rd inning of a 3-2 game - or wind up with a series of "call stands" indecisive review calls after taking 30 seconds to stare at a graphic on a jumbotron. I don't think borderline ball/strike calls need to be reviewed ad nauseum - limiting teams to 2 reviews per game helps to keep that in check, and as others have said as long as challenges made are correct, teams could in theory challenge dozens of calls a game if an ump was truly that bad. At that point, if game time becomes a problem with the reviews, the solution should be to replace the umpire making all the bad calls.
And I love the idea of players getting a dose of reality for those times they want a call reviewed that was obviously correct the first time. Not only does that help reset their own perspective, it hurts their team for later in the game by burning up a challenge.