The next-gen Xbox (aka 720... aka Durango) is in devkit form already and that kit is apparently being traded online if several sources are to be believed.
The kit was put up for sale on a developer forum called Assemblergames
with the person selling 'Durango Devkit' valuing it at $10,000.
DigitalFoundry tracked down the seller - who calls himself @superDaE
on Twitter at least. The DF chaps looked over some blurry images purporting to be the kit (one pictured in this story) and report
"The obvious conclusion drawn by many was that it was an unambiguous fake. Intrigued, Digital Foundry reached out to the source of the leak, and followed up the story with multiple developers working on next-gen projects. The uniform response was startling: apparently, these shots are the real deal."
Also reported is that, "Beyond that, further information is sketchy and unreliable. DaE reckons that the current devkits were dispatched to studios in February, and feature Intel CPUs and a graphics card that carries the NVIDIA brand - but he doesn't identify either part more specifically. He also claims that the Durango kit features more than 8GB of memory (other sources have suggested 12GB), and that it is 64-bit in nature - at this point it's worth bearing in mind that dev hardware typically features double the RAM of retail kit in order to accommodate debugging tools and other systems. DaE also says that Microsoft is targeting an eight-core CPU for the final retail hardware - if true, this must surely be based around Atom architecture to fit inside the thermal envelope. The hardware configuration seems difficult to believe as it is so divorced from the technological make-up of the current Xbox 360, and we could find no corroborative sources to establish the Intel/NVIDIA hook-up, let alone the eight-core CPU."
Devkit in the wild clearly indicates that we're now operating beyond mere speculation when it comes to Xbox NewGen/720/Gen 4/Durango.