Prison of Elders Predictions?

Bungie just posted their teaser for the Prison of Elders Twitch stream. In 24 hours, we will know what it will have in store for us. Anyone care to guess or predict what we'll find, besides the general "horde mode" guesses? I'll start by going out on a limb and making my own prediction: Bungie has emphasized that the Prison of Elders will excel over previously expected content (i.e. raids) in the area of re-playability. The ultimate way to make something re-playable is to generate a different experience every time. I'm hoping that Bungie will go beyond the trivial modifiers we've seen in nightfall and move to procedurally generated content - possibly labyrinth-like or obstacle-laden maps that are algorithmically generated and different every time. Perhaps randomly rolled enemies. Objectives or goals that vary from one playthrough to the next. Their term for this new mode, "Arena", suggests a limited, confined space - which would be ideal circumstances for code to generate variance within. That's what I'm hoping and predicting; anyone else have any thoughts?