So that headline's probably stating the obvious. I would imagine there are lots of studios working on something besides what they've already announced.
The recent interest stems from a digital resume someone posted on LinkedIn and pointed out by Superannuation. The resume, said to be for Ross Nicoll, breaks down the current audio design lead at Ruffian Games' experience.
Here's the summary:
Started out At VIS Entertainment in 2003. Moved to Realtime Worlds in 2005. Member of the Crackdown audio team that won the 2007 "Best Use of Audio" BAFTA award. After Crackdown, I worked on APB, and another unannounced project. Left Realtime in Feb 2009 to take on the role of Audio Design Lead at Ruffian Games - www.ruffiangames.com
Credited on the following titles:
Crackdown - Xbox 360
Brave: The Search for Spirit Dancer - PS2
The Powerpuff Girls: Relish Rampage - Nintendo Game Cube
Tom and Jerry: War of the Whiskers - Xbox
Another interesting point: Rumors have been floating about that Ruffian Games was formed to work on Crackdown 2.