Infinity is busy with Call of Duty: Ghosts as they didn't want to just keep adding sequels to the Modern Warfare series. That means it's wide open for another studio to play with.
Sledgehammer is no stranger to the Modern Warfare work over at Infinity Ward as they worked closely together on Modern Warfare 3 following a certain staff exodus.
Infinity are exploring a "completely different universe" with Ghosts, so it would seem the Modern Warfare torch has been passed along to Sledgehammer, if this LinkedIn profile proves accurate. A Google cache keeps the from Rob Valdivia's profile.
"I work at Sledgehammer Games where I'm responsible for developing photo real visual effects for the next Call of Duty - Modern Warfare release," Valdivia originally wrote. It's suggested that Modern Warfare 4 will be 2014 bound, but of course Activision offers a wall of silence on the matter.
Multiplayer for Call of Duty: Ghosts is expected to debut next month.