There was Azrael's appearance in Arkham City where he gives cryptic warnings that just scream "sequel". His exact words were:verdant monkai said:Wasn't Arkham city supposed to be the last game? But then Arkham Origins got made, and now there's this game...
Something tells me we haven't seen the last of the Arkham franchise yet.
"I bring a message: dark days are coming, Batman. The Prophecy is coming true, you are the warrior who will close the gates of Hell, you are the one who will save this day, and in doing so, events will occur that you cannot stop, from the ashes of Arkham the fires will rage and Gotham will burn, and you, you will burn too."
So presumably Arkham Knight will be about that.