The game is apparently said to be a prequel to the previous two games in the series. However, it will still be developed by Rocksteady Studios. It would seem that the story would somehow be linked to the Batman comics of the 1950s and 60s. Along those lines, Justice League of America members Superman and Green Lantern will also be connected to the game in some form.
Furthermore, unnamed sources are continuing to claim the game will be out in Q3 of 2013. This seems to be in line of the financial call earlier this year which hinted at a new release.
The game will focus on the time when Batman first encounter Joker, around the time when the Justice League is first formed. There’s no concrete information regarding a release date though. Some speculate the game will be released sometime in 2014, others state it will be much later.