Well known for his vocal talents in the Arkham games and the Batman Animated series, Kevin Conroy (the voice of The Batman) did a little interview with the guys over at Groovey.tv. During the interview they discuss the fan base and how Kevin originally got onto the role. Near the end of the interview, the topic of Batman: Arkham Knight comes up and Kevin Conroy had this to say:
It was supposed to come out in January, we’ve been working on it for a year and a half, its still not done. So its going to come out next January.
View the interview in its entirety below, the game is brought up near the five minute mark.