While this all comes with the usual grain of salt, the penultimate issue of Xbox World magazine boasts an 8-page feature that details Microsoft's next-gen Xbox console. The feature goes on to dig into the system's introduction of Kinect 2.0, use of Blu-ray discs, 3D sound, "innovative controller," augmented reality, and more.
Xbox World speculates that Microsoft's new system will simply be called "Xbox," and says that current dev kits codenamed Durango feature a CPU with "four hardware cores, each divided into four logical cores," as well as 8GB of RAM.
An interior image, from CVG's post:
Xbox World EIC Dan Dawkins comments on the story: "Xbox World has been at the cutting edge of Durango coverage for over 12 months… Unless something really dramatic changes, everything we reveal in our penultimate issue will be revealed long before E3 in June."
Similarly, PSM3 has a whopper of a speculative feature on PlayStation 4.