Well, Arkham City was announced only a few months after Asylum was released, I think it was in December, 2009 (and Asylum came out in August or September of 2009 if I recall correctly), so I wouldn't be surprised to get official confirmation from Rocksteady about the next game in the series in the near future. As for it being called Arkham World, while there's an obvious logic and progression for both the titles and story, its just clunky and stupid as a title. We'll see.
I agree that was my thoughts. I don't like title as it doesn't work but still want one.