I've been advocating for years that tennis-style replays are the way to go with a limited number (5) of reviews per team per game. Goal should be to weed out the really bad calls but still allow some human element (such as rewarding a hot pitcher for consistently hitting the corners). Each review should take no more than 15-20 seconds. Hitter or pitcher calls for review (has to be immediate and can't be called from the dugout), umpire points to the press box, someone presses a button, and the pitch f/x animation plays on the scoreboard. Alternatively, the stadium experience would be really interesting with the full 'pitch tracker/gameday' interface available to fans on the scoreboard. Under that scenario, humans could still call balls/strikes but the scoreboard could automatically overturn any egregiously bad calls. If the pitch is right on the corner, the right course of action may be to default to the human anyway based on the uncertainty in the pitch tracking.