JJ Abrams is coming off the back of a huge hit with Star Trek, and can pretty much name his project in Hollywood. When the director spoke to TV Guide recently, he indicated that he has been asked to return to the Mission Impossible franchise by star and producer Tom Cruise. Abrams has not yet committed to the sequel, but at the moment it's looking like he'd produce at the very least. MI:3 was seen as something of a financial failure by Paramount as Cruise's deal was so huge, no profit was made - this despite the film winning mainly positive reviews and doing solid business. Abrams' return would be a huge scoop for Cruise, regardless of his creative capacity on the project. I don't think he'll direct, though.
