While I certainly understand the appeal of having Shepard be the main character the story, the fact remains that Shepard wasn't really much of a character at all in the games. Sure, she made decisions based on choices, but there was never really a story arc that gave her a sense that she had changed as a character. Once she commits to stopping the Reapers, that's all there is to her till the very end.
This is why other characters in Mass Effect work way better than Shepard does because unlike Shepard, they have Arcs. They have character development. They do change their stances. Shepard just isn't that much of a character.
Yeah, see, I'm working under the bold assumption that a Mass Effect movie would actually have a script
, and not just be some guy's playthrough. Shepard could have just as much character development as needed.