If you google "Halle Berry X-Men Days Of Future Past" you'll find dozens of pages worth of finds on the subject. Apparently, in December and January the word on the street was that Bryan and Fox were pursuing both her and James Marsden to join the cast. Even The Hollywood Reporter did an article on it. The articles said that the actors were more willing to get on board since Bryan was at the helm again, so that should squash any "beef" rumors between Halle and Bryan.
It would be a major missed opportunity not to have Storm in this film, since she plays a pivotal role in both the future and the past in the comic. Besides by time DOFP comes out, we will have had at least 3 X-Men films without Storm in them...waaaayyy to alienate a major fanbase section of X-Men fans.