Octogunspunk said:
It's a bit late for that now...
Might as well just introduce a new character, really. You're not going to be able to give a man whose image is overwhelmingly a mute, power-suited supersoldier much personality without horribly dividing the fanbase. As is the case with a lot of mute protagonists, they are solely a vessel for the player's personality.
The misconception is that, Master Chief was never a mute, he always spoke, just not during gameplay.
8 minute mark and on, you see MC talking.
OT: It will be hard for them to explore much of his background, well since, it already had been in Fall of Reach, where it showed his origin. I guess they could show ingame events of parts of the origin.
Or just show us the personality he had in the book more.