According to Jayson Stark on Mike & Mike In The Morning today, and recapped in Business Insider, replay is finally set to expand in 2013.
Stark reported there will be umpires in a central location double checking close plays to let the umpires in the game know if they need to correct a play. A review-specific umpire has always seemed to make the most sense. Many fans complain about the fear of the games slowing down, citing the NFL's approach to replay, but there is absolutely no reason baseball has to simply copy the NFL. A replay umpire can look at the play in seconds, without anyone having to leave the field.
Stark mentioned the replay will initially be used for home runs, fair/foul calls, or caught/trapped plays, and will then be expanded after testing. That expansion would most likely encompass some of baseball's biggest frequent mistakes, like incorrect calls on the basepaths. How exactly rules will adapt for replay, or how well umpires will actually do at calling out other umpires remains to be seen.
At the very least, though, this is some of the most exciting news baseball could manage. It's a crime it has taken this long for them to utilize the extensive technology available to them in order to make sure calls are actually correct, but at least it is happening sooner rather than never. On top of that, they're doing it with a smart approach, and minimal intrusion on the flow of the game.
Now ban silly manager arguments over replayed calls.