First up, the insidery, anonymous MS Nerd blog is reporting that the next Xbox, codenamed loop, will run on a modified version of Windows 9 and use ARM architecture. The custom designed hardware will supposedly feature "a 'main' processor with multiple dedicated assistive cores for graphics, AI, physics, sound, networking, encryption and sensors." The blog adds that the device will be "cheaper" and "far smaller" than the Xbox 360.
Meanwhile, on a recent episode of TWiT's Window's Weekly netcast (at 1:28:15), Paul Thurott of Supersite for Windows offered a slightly different take on the console's prospects. First of all, based on his own sources, Thurott is expecting a holiday 2012 launch, meaning Microsoft "would almost have to announce this at CES" in January. Further, the system will utilize the same Metro UI design as Windows Phone 7 and will feature "embedded Silverlight." Furthermore Thurott says the console will go "the Apple route" and will "integrate very tightly" with Windows Phone and Windows 8.
In summation: The next Xbox will release in 2012, 2013 or 2014, it will have processors, run Silverlight and will use either Windows 8 or Windows 9. Hopefully that clears everything up.
Microsoft Xbox One