The people at Fox are apparently very interested in creating another film in the X-Men franchise.
Brett Ratner has gone on record as saying that he would definitely be interested in directing the new film (and has perhaps been offered the opportunity?)
Ratner said, “It [an “X-Men 4″] wasn’t in the plan, but I loved the experience of it, and I loved all the actors, and I would definitely do it again if they asked me to come back. I had that little thing [at the end] where Magneto moved the [chess] piece. Did I want to see a sad, old pathetic man who lost his powers in a park? Did I personally want to see some hope? Yeah. It wasn’t because of the fans, I just wanted to see it. Is it mind over matter, or is it the power? Poses a lot of questions.”
Any official announcements concerning X-Men 4 may be far off from now. Fox has both a Magneto spin off in development, as well as a film based entirely on Hugh Jackman’s Wolverine character.