After quitting Bungie Studios at the end of September 2013, Halo and Destiny universe co-creator Joseph Staten has returned to Microsoft. His new post is senior creative director, and he joins the Xbox team to help create "incredible entertainment," according to his LinkedIn page.
Staten is a prolific Halo writer, having written for every game in the series developed by Bungie. He also served as creative director for Peter Jackson's Halo film (which would later fall apart) and authored the New York Times bestseller Halo: Contact Harvest.
Staten's current Xbox project at Microsoft is unknown.
It is possible that he's working on one of Microsoft's numerous unannounced Xbox One projects, or even potentially the new Halo game. He did, after all co-create the Halo universe, making him a likely candidate to guide its future.