Once you finish the narrative in TTK (story,raid etc) you will unlock a mission that explains what happened to Praedyth in the VoG (it's in the vault as well) and where he is now! I'm so excited for TTK! If your negative please don't comment thanks.
This was confirmed by Game Informer Magazine
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I played it, its pretty cool and it can be tough if you don't end it quickly the enemies will very rapidly get out of control, just make sure to hit that thing with everything you have when its vulnerable and you'll be fine.