Seems like the deleted scenes are only available in SD on Blu-ray:
[blu-ray.com said:]
Enhanced Viewing Mode allows viewers to watch a version of the film with deleted and extended scenes inserted into the film. Also available is a selection of 17 behind-the-scenes pieces that may be viewed during the film by pressing the “1” button on the remote when an “X” icon appears on-screen. Finally, an extended commentary track is available when watching the movie in Enhanced Viewing Mode. All of the deleted and extended scenes are also available through the Enhanced Viewing Mode tab or the Deleted Scenes / Extended Scenes (480p, 11:02) tab of the main menu, while the behind-the-scenes features are accessible instantly from the Enhanced Viewing Mode tab.
Source: https://www.blu-ray.com/movies/X-Men-Blu-ray/3736/#Review