Ken Rosenthal has a story about MLB considering a proposal to expand the use of instant replay for reviewing questionable calls by umpires during the playoffs.
Of course, this being MLB, it isn't something as straightforward as having a fifth umpire in the booth who has the authority to review and overturn calls on his own. No, MLB is apparently considering instituting a "challenge" system, so instead of there being controversy over a blown call, there can be controversy that a blown call wasn't able to be overturned because Fredi Gonzalez or John Farrell threw his challenge flag out earlier in the game.
Assuming the proposed system is approved by the owners, the umpires union and the players union would still need to approve, so there is no guarantee it would actually be implemented this October. But still, this is at least a step towards getting more calls right, even if its within the weird challenge mechanism.