The tagline is "Arkham has moved". I think this is a play on words that the Joker simply took over a part of the City and filled with Arkham Inmates. So "Arkham has moved" outside.

On that note, "Arkham Asylum 2" is a fitting name.

That, alone, gives you some of the scenarions. You have the Streets, you have the old ruins of Arkham, the Swears, the bay that showed up in the ending of Arkham 1... i would bet this game makes you visit the Police Station too. So you'll probably have Killer Croc and Scarecrow back there... i'm Guessing Mr Freeze as a new Villain, and, an excuse for a Ice Level (probably Arkham Ruins)

I don't think they would use the "Joker dies" Gimmick in this game though, he is clearly very sick due to the side effects of his last fight with Batman and still recoverying.

Occasionally there is a comic to this effect but lol comics.
 

To say Batman made Gotham a better place you pretty much have to assume that without him it'd be goddamn Roanapur.