People actually feel the blond hair was a mistake? I couldn't even remember his hair color...Are there no blonds in England?
Anyway, if the Master does come back, I'd like them to acknowledge the events of "The End of Time" and have the Master do some reacting/soul searching. I'd ultimately like him to go back to what he's always been but you can't learn that your identity was based on something that turned out to be somebody else's meddling and not have an identity crisis. This seems like the perfect oppourtunity to have Simm explore his idea for a darker "Master".