Batman: Arkham City followed about two years after Arkham Asylum, which means we're about due for another game revolving around Gotham's favorite insanity hotspot. Warner has confirmed that another title in the franchise is due this year, though it hasn't given much else in the way of official info.
"We also have a strong games release this year, which will include the next release in the Batman Arkham franchise," Time Warner CFO John K. Martin said in an earnings call. It's unclear if Martin was referring to the calendar year or the fiscal year, the latter of which could go into March of 2014.
VG247 also cites sources claiming that Rocksteady isn't developing this game. We had previously heard rumors that the next Arkham game would be a prequel set in the Silver Age, detailing Batman's first confrontation with the Joker. This was purportedly part of an effort to team Batman up with other DC heroes, as was common practice during the Silver Age of comic books. That report also claimed the game would not be coming until 2014 at the earliest.