Yes and no. In the sense of "expanding" D1, yes. Using the same weapon, loot and level systems. With new strikes related to the new storyline and all. However, in the sense of being a DLC, no. The original's code was already too messy since Bungie changed something (nerfs and buffs) almost weekly. Proof of that is that Bungie says that everything is "working as intended" but D1 is full of glitches. Mostly, the kind of glitch that forces you to wipe, not "useful glitches like Swords on Oryx's totems or Crota's bridge. These bungie fix ASAP. Last week, we were doing Vosik's challenge, and two of my teammates got shot by Vosik inside the closed rooms and died. Not to mention the years old Crota's glitch that makes the sword disappear as soon as you pick it up.