Helen McCrory to play young M in Skyfall?

Actress Helen McCrory has been cast in the new James Bond movie, Skyfall, but her role has not yet been announced. Although there are rumors that she'll be playing Miss Moneypenny, wouldn't she be perfect as a young M (who is played by Judi Dench)? Part of the plot of the movie is that "Bond's loyalty to M is tested as her past comes back to haunt her", so it would make sense for there to be flashback scenes with a young M.