Michael Bay just made the following post on his website
TMNT: we are bringing Megan Fox back into the family!
The movie is scheduled for a May 2014 release, more info as it becomes available
More info just in Megan will be playing the role of April O’Neil, the movie is set to start filming April this year in New York and Bay will be producing not Directing so he will be less involved with the actors in a day to day basis. So Them working together is a little less surprising now that I think about it
Some info on how their reunion came about
Sources say Fox and Bay reconciled over a series of recent meetings and that one tete-a-tete that won her over was with director Jonathan Liebesman, who wowed her the storyboards, according to insiders.