So I managed to finish ODST on Legendary tonight. And post ending, post epilogue, we're treated to a shot of numerous Covenant Engineers hovering near the Superintendent structure. Then, the Prophet of Truth levitates down from the vertical tunnel and inspects the area. The camera pans to what looks like some sort of Forerunner architecture stretching from behind the Superintendent structure. Truth gazes at it, then sort of moves his hand toward it like he's content with what he's found. 
 
But I'm not quite sure what he's found. I refuse to believe it's just the underbelly of the Portal, but if that's the case, then it's something not at all established in Halo 3.
 
Any ideas? Something we're going to learn more about in further installments of the Halo franchise?

I think its just him discovering the activation thing for the Ark portal. Considering the last Bungie installment is going to be Reach a prequel and the placement in the timeline of the end of ODST that is the only logical choice. It would be hard for whoever takes over the Halo franchise after Reach to piece that epilogue into something we havn't seen yet. Truth is dead and we have seen the importance of New Mombasa in the plot, there is nothing else they could do with that. Well nothing that would make sense and be interesting at least.