According to a recent tweet, Singer has three new ducks: He has just acquired the talents of Anna Paquin, Shawn Ashmore (both in X-Men, X2, and X-Men: The Last Stand), and Ellen Page (X-Men: The Last Stand), who played Rogue, Iceman, and Kitty Pryde, respectively.
FORBES: Anna Paquin, Shawn Ashmore and Ellen Page Are On Board for 'X-Men: Days of Future Past'