This is likely be a popular choice. It certainly seems like a safe one. Horn was president and COO of Warner Bros. during a period when that studio churned out franchises like Batman and Harry Potter. He's also a known quantity, which will be a contrast to his predecessor, Rich Ross, who had limited experience in the film world (he was more of a TV guy). From the LAT:
Horn will be under enormous pressure to bring stability back to Disney Studios, which was roiled by management upheaval and box-office troubles under Ross. Under his tenure, the studio took a $200-million write-down on the costly sci-fi adventure film"John Carter." "I'm incredibly excited about joining The Walt Disney Company, one of the most iconic and beloved entertainment companies in the world," Horn said in a statement. Horn was pushed out of Warner Bros. last year after a largely successful 12-year run.
From the NYT:
Horn reluctantly left Warner Brothers last year -- indelicately squeezed out to make room for a new generation of managers. While running Warner's movie operation, he drafted the blueprint for an operating strategy that has been adopted by virtually every major studio: focus on effects-filled event pictures, or "tent poles," that resonate overseas. Along with his careful steering of the "Harry Potter" franchise, Mr. Horn's hits include "The Perfect Storm," "300," "The Departed," "Happy Feet," "Ocean's Eleven," "Sherlock Holmes" and "The Dark Knight."