Hopefully baseball will remain (mostly) instant replay free.
The greatest thing about the greatest sport is that it is the personification of human nature, governed by humans. Failures and all, I would much rather keep it that way.
considerng MLB claims at HQ that umpires are report carded, I find it odd that if they make enough mistakes, they aren't demoted to the minors to umpire (and bring up a more capable umpire from the minors). AFAIK, umpires just aren't given the big gigs (all star game, playoffs, etc) for a high rate of error.
What I would like to see is automated balls and strikes - you can take away a lot of the balls and strikes argument that way. find the average MLB player height, rule book the strike zone dimensions based on that rather than based on the batter's body, and set up and calibrate your robot sensor to detect when the ball is inside the strike zone box or hits the edge for a strike and when it misses the box for a ball. easy with today's tech and quicker than a lot of umpire's ball/strike decisions!
umpire stays at the plate for HBP decisions, swing decisions, foul/fair decisions and home plate safe/out decisions.