Having some personal friends who have worked on large productions in the entertainment industry, it's not uncommon for management to change at the last moment. Nor is it uncommon for writing teams to have multiple people on them. I have long speculated that when Bungie signed that deal with Activision, they realized they had to all of a sudden meet a ten year obligation. They likely built their game for a one off release with the intent to add to it over time. But then the Activision contract hit the table and new obligations were made. The original story may still be intact, but they went the Anime route and decided to make filler episodes to meet these new obligations on time and in a manner that was consistent with their contract obligations. Biggest reason I say this is because of how Bungle is approaching Destiny now that they are no longer a part of Activision.