Bungie is already at work on the follow up to Destiny, according to an insider. The game is said to be called Destiny 2: Shattered Suns, and based on the info gathered by this insider it is going to be written down by Hollywood script makers in order to focus more on story.
Furthermore, and this is where we hardly believe to the intel coming from the insider, Activision and Bungie are working on a new free additional content model that will replace DLCs as intended today. It could be something subscription-based like Battlefield Premium or the old Call of Duty Elite.
Shattered Suns is said to be coming on September 2016. Here you have all the info arriving from the insider in one place:
"Now for Destiny 2.0, this will be a completely new game. It is titled currently as "Destiny 2 - The Shattered Suns" and is planned for release on September of 2016. You will still be using your current characters. It will focus heavily on Osiris and his endeavors as he is the main quest giver in the game. A new form of enemy is said to be in development, Possibly Ahamkara? Couldn't get a straight answer from anyone on that.
Mercury is also supposed to be a big player in "Destiny 2 - The Shattered Suns". The main area in which the guardian will explore. Bungie has also hired on Hollywood writers for the story of this game as well. A new voice for the ghost is also being implemented. Bungie apparently stated that they are not going to continue with DLC's, but instead release free raids, planets, etc. throughout time. They will only be continuing with the main games after TTK and its successor DLCs.
Finally as a bonus, there is not going to be trading implemented into the game ever. Stated,"Activision got sent a letter regarding what not to do on a mmorpg from Blizzard, and trading was on that list". Also that there is no 6th chest in the VoG or has only been known by a small group of people in the studio. It was just a bluff to keep us occupied for The Taken King most likely."