The online portfolio of industrial designer Ben Peterson lists all sorts of projects he's worked on or is working. One of those is apparently the next Xbox.
His portfolio reads:
Microsoft Xbox: Confidential / Collaboration with Microsoft's IEB Design group investigating future user experiences and hardware for 2015. *Work samples only permissible in persons.* (March 2011)
Website ZDNet believes that the March 2011 dating means that the project has just got underway. By 2015, the Xbox 360 would be ten years old, making it an ideal time for a new consoles. However, it is unconfirmed whether Ben Peterson is involved or not in the next Xbox.
Microsoft, and all electronics companies, are always working on new machines. What form they take if and when they make it to the market is another issue altogether.
Kotaku is following up with Microsoft and will update this story should the company comment.