I would have like that for replay in general, instead of manager challenges. Just let the umps on the field make the immediate call, but have an ump in the booth who can buzz an override to his colleagues if something is worth closer examination on video. Not sure it works on balls and strikes, though -- there are so many borderline pitches, I think you'd have players constantly making appeals, hoping to get the attention of the ump in the booth. Whoever makes the initial call there has to have final authority, I think. Just go full automated strikezone so the ump is simply delivering that call, no appeals or overrides are necessary, and you keep that authority but you also gain the accuracy.