Huh. Looks like my hopes have been realized. Thanks to Kotaku and their "source", who decided to spill after Game Informer broke the news, Batman: Arkham Asylum is indeed in development by Pandemic, though oddly, EA has not been confirmed as publisher. As I has suspected, the game is a third-person, open-world action romp and it's set in a GTA-style rendition of Gotham City, which plays a lot like Spiderman 2 as Batman zips around (he even gets a grappling hook for swingy-swingy when not using the Batmobile) attending to crimes.
Interestingly, this may very well be the game that was, um, "referred to" in the above video. Apparently, Arkham Asylum is not based on the comics, but on Christopher Nolan's Batman universe, only the game takes place after The Dark Knight ends. Hmm. To be fair, it was never actually stated that the game Mr. Gary Oldman had seen was a direct movie-to-game translation, like so many others. This could work.