So basically they'd combine Lulu and Spinzaku, hero has to be the ultimate warrior. They'd drop the whole Nunnally character, because cripples are a total downer. Kallen and Euphie would be combined, regular old spunky princess fighting under an assumed name. Charles would be the good emperor that has been deposed by the real villain: Orange-kun.
The movie would conclude with Luzaku defeating Orange in an epic 15 minute long one on one fight in front of all the main characters, possibly broadcast live all over the world. He would then marry the princess and become the benevolent emperor.