I feel Kaneki's obviously acting like Arima is just a ploy. Granted, I think his ruthlessness and power are his own, the glasses and his compliance with the CCG are a ruse. He has an agenda, and once all his pieces are in place, he will show his true self. What ever his plan is, he needs the CCG trusting him. So, why not act as Arima's puppet. His personality has changed to obviously for him to play Haise, so why not become what they want him to be - a weapon.
Hori was right, if Kaneki wanted to kill Shuu, he would have. If Kaneki was, in all sense, for the CCG, he would have killed Shuu that night. He didn't for a reason. He stayed with CCG for a reason. What that reason is...well it may take another 50 chapters to see.