This probably isn't true at all, but DigiTimes reports that Microsoft is already readying a new version of the Xbox One. Even more is that it may be released in early 2014.
While Microsoft will launch the Xbox One on November 22, it is preparing to introduce a new version of the Xbox One in the first quarter of 2014, according to Taiwan-based supply chain makers who say they have been asked to begin shipments of the new model in that quarter.
Shipments of Xbox One from the manufacturing side began at one million units a month in the third quarter and monthly shipments have been increasing in the fourth quarter, the sources indicated.

If this is at all true, I wouldn't expect it to be any major revision and probably shouldn't impact your buying decisions.