Board Thread:Speculation House/@comment-4830106-20140806180925/@comment-6863431-20140830050917

Just remember that Zuko only turned because he was turned on. Before that, he was going out of his way to murder a twelve-year-old child.

Besides, Zuko's motivation was always for honor, while I doubt that Mercury is driven by something so redeeming. I have more of the feeling that he's driven by the thrill of fighting, which Cinder is happy to offer him. If Mercury does turn, it will be because he was either tossed aside by Cinder or betrayed by Emerald.