I'm not even sure why people think it's going to happen, at least in the next three episodes.
How can it not? We know that there will be a trial by battle with the mountain fighting for Cersei and someone for the faith.
Can't believe that won't be the Hound. He's about to murder those knights and then what? He wants to do something good, he seems to believe what McShane said to him - at least to a point. And he wants revenge. What better way to get it then to fight his brother and therefore kill the queen?