Master Chief is still lonely
343 Industries is currently in the midst of working on the next iteration of the Halo franchise. Unfortunately, without the 5 after the title, there is no guarantee where this game falls in the series cannon. The clues of a wandering Master Chief clutching at Cortana's chip does indicate that it this next game take place after the events of Halo 4.
With the addition of dedicated servers for "cloud computing" and a smooth 60 frames per second, 343 is really looking to out due themselves. No release date has been announced yet.