Except it wasn't a concept? It was actually in the game. E3 gameplay is supposed to reveal what the developers are working on for the game that is to be released, to get people to buy it, or build hype. If those things weren't going to be shipped with the original game, then why show these things and why have them in the game and being used, an entire year before the game is released, and 2 years before that "DLC" was released?
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Because they scrapped the original story sometime shortly before release, remember that story writer that left bungie. With that done and the story writer out bungie scrambled to piece together the Frankenstein game we know today as destiny. Some one like Osiris that isn't even in the game now was supposed to play a huge role in destiny's original story.