X-Men 3 is 20th Century Fox's Top Priority !
At this time also the character of Storm is getting included in the screenplay. But the screenplay will be written, so the character can be switched to another, if Halle Berry won't come back to reprise her role as weather controlling Mutant. There are also plans to expand the role of Storm to that equal of the other characters. Everything is open at this time, so it also can be, that Storm casts a new actress or just a small cameo.
Avi Arad and Marvel listed a May 2006 release, and at this time nobody wants to think of a winter release 2006.
At last, there are some rumors, that the next Spin-Off movies could be Mystique or Storm movies, but as i said, this are only rumors for now.
There are still no confirmed informations about who will direct the movie, or what the storyline will be.