Sadly, it doesn't look like Mel Gibson will have anything to do with this project.
Back in 2007, Miller had this to say about Gibson's involvement in the film, "I don't think he would be interested in being involved at all."
It seems that the director wants Tom Hardy (Black Hawk Down) to co-star with Theron.
Lastly, Miller is also being "very secretive about the roles and plot." The talent auditioning "for the film have only been given a letter for their character's name. The studio has yet to sign off on Miller's choices, and no formal offers have been made."
At present, all of the above information is just rumors.