According to Edge magazine's sources, Ubisoft Montreal is already developing content for the Xbox 360 successor using "target boxes" that are designed to emulate the system's intended specs. The same source also said that they expect to receive the first genuine dev kit before Christmas.
Those target boxes are said to be PCs that contain off the shelf components as well as GPUs from AMD. There are also reports that other developers such as EA are also in obsession of target boxes.
Edge magazine also revealed with absolute confidence that one major Sony-owned studio has now ceased PlayStation 3 development entirely, shifting its focus to developing content for its successor.
It is reasonable that Microsoft and Sony don't want to give Nintendo's Wii U a considerable head start, but is there really need for new consoles now?