On February 17th the game will be revealed. Visit Bungieto read more about it.
Its their new IP that will be released for Pc and Next gen gaming. It will be MMO game that takes place on the future of our planet Earth. Years after exploring the space humans are now pushed back to Earth and there the action will take place.
On another guess, could this be Titan? Blizzard passed the development to Bungie or Co develops it?