Honestly, the book is so complex that you really can't make an accurate film of it, and EG is the least complex of the Quartet. I'm fairly certain they'll keep the Bonzo fight in, and why would they cast Stilson if they weren't going to have a major conflict? As to Graff and Anderson, they have two stars playing them, so Hood would be a little silly to have their roles cut down. Honestly, they'll probably cut out portions of the Battleroom; it's less important to the story of Ender as, say, the fantasy game, or training with Mazer. A montage scene of Ender winning battle after battle with Dragon would be sufficient, whereas the book goes into three battles in fairly heavy, though quite enjoyable, detail.