"Although Brad Bird's Mission: Impossible IV has yet to be officially greenlit by Paramount, Heat Vision is reporting that actor Simon Pegg is already in talks to return as lab geek Benji Dunn in the movie targeted for a December 16, 2011 release.
Pegg's role in J.J. Abrams' feature film debut Mission: Impossible III was a fairly small one, but it ultimately led to Pegg playing Scotty in Abrams' blockbuster reboot of Star Trek last year. With Abrams producing the fourth installment, it would be Pegg and Abrams' third movie together before the in-development Star Trek [sequel].
Once Paramount gives the go-ahead, plans are to start filming in September with Tom Cruise already signed to return as Ethan Hunt."
Obviously, Paramount is worried that the public has lost interest in Tom Cruise. Especially when he tried to throw audiences a bone by being both funny (like he did successfully in Tropic Thunder) and action-packed (again, as in the M:I III) in the box-office flop Knight and Day. Paramount fears that Cruise can no longer pull in an audience, because of all his personal controversies. They have been conspiring to basically turn Mission: Impossible IV into a Kingdom of the Crystal Skull-like film - aka getting him a younger, more BANKABLE sidekick. Somebody they know audiences will pay money to go see.
I think it would be kinda cool for somebody like Simon Pegg himself to play the sidekick. Almost like the TV show "Chuck", a tech nerd suddenly thrust into the world of being a spy; but on a much larger scale. But that's just me.
On a live Comic-Con special on G4 with (the vivacious) Olivia Munn, Simon Pegg (promoting Paul with Nick Frost) admitted he hasn't actually signed a deal yet, but wouldn't mind returning.