According to ThisIsXbox.com, they were lucky enough to be seated in a flight right next to Cpt. Price himself, Billy Murray. It appears during the flight, Mr. Murray let it slip that Infinity Ward is hard at work on a sequel to MW3. You guessed it, Modern Warfare 4..
“Yeah, on Monday I am off to meet Infinity Ward about the next game, Modern Warfare 4, I’m doing work on the sequel to Modern Warfare 3, it carries straight on and I only ever appear in the Modern Warfare games…”
*Supposedly the photo above [Billy Murray & ThisIsXbox] was taken right before he discussed MW4
UPDATE: Infinity Ward has confirmed that the rumors are NOT true.