So I guess a couple weeks ago it was confirmed that a new Arkham game would be released later this year. I just got finished playing through a bunch of the downloadable content for Arkham City, and I am more than ready for another installment.
Points of interest: It looks like Rocksteady will not be developing this new sequel, which could end up being a good or bad thing (who knows?).
There were also a rumors of a new Silver Age Batman/Justice League prequel, which may or may not be this new Arkham game. I personally hope that they are different games, as Arkham City's story did certain things that set it up for a continuation.
If they want it to be a multi-character game, I'd rather they do what they did with Arkham City by including Catwoman. You could also throw Robin or Nightwing in there if you want, but I'd prefer the story to be solely in the Batman universe.