The Helfire Club could be a strong contender along with Dark Phoenix as a member of it. 'Cos during X2 Xavier visits Magneto and and Magneto is reading The Once and Future King which is about king arthur and his returning in times of need.This would be the perfect setting for Magneto to RETURN as White King of the Hellfire club in the next film as this would cut down on screen time explaining his contection and reasons for being there. As for Jean Grey the best would be skip Phoenix and go straight to Dark Phoenix as the Black Queen, as this would be bending the comics story line within reason as Lady Deathstrike and Archangel were meant to be Weapon X subjects in X2 wich doesn't follow the comics
Most Wanted for X3
Archangel and Gambit
I think that legacy virus thing sounds cool but it would look a bit like Resident Evil. It actually doesn't matter to me what they do with the next movei as long as they keep it real and nothing too fantastical. I read somewhere in the X-Men section that someone wants to see Bobby Drake in full Ice figure. I know that looks good for a comic book but not for a movie. I aslo don't like the idea of the sentinels. I dont know much about the X-men history but i know that somethings are really bad movie material.
And something for you guys. more than two characters have signed on for X3. Only a few mayor characters have not like Hugh JAckman and Halle BErry.