I noticed there's an eye and a mouth on his kagune as people had mentioned it.
I wonders his kagune can create a doppleganger. I would picture the doppleganger will turn out to be Haise Sasaki.
If Kaneki will contniune the darker path in the rest of the series and starting hurting friends, I would see Kaneki created him out of boreness or Kaneki's body got split into half by Arima (or possibly Amon) and his lower half will end up create Haise. I would picture Haise will betray Kaneki as the Black Reaper and end up joining :Re to protect them from Kaneki. Probably he will learn a lot of stuff from them. I think he will against Kaneki,because maybe he will realize that Kaneki thrown his emotion way and the people that he care about for powers. I think Haise will be only one have remaining of his emotions that left behind.
I think it would be cool if Ishida do that to make Kaneki Vs. Haise (as in physical form if he creates from Kaneki's kagune) fight in the near future.