While previous rumors hinted at a 2012 reveal for the next Xbox, new reports indicate that it may be held off until 2013. Develop has heard from multiple industry sources, including chip manufacturers and middleware firms, that the console's reveal will come at E3 2013, with a late 2013 launch to follow.
The launch would likely be simultaneous for all territories, but that doesn't necessarily rule out a 2014 release in some countries. The initial launch is expected to come by the 2013 holiday season, but few analysts expect it to come any earlier than that.
Develop also reports on several other rumors that lend credibility to an upcoming console launch. Namely that Lionhead Studios is currently working on a project known internally as Fable Next, which is expected to launch on a new console. Another source reports that EA has rudimentary next-generation console technology already (which EA has denied).