The pyramids on Par Vollen (created by ancient humans, apparently) depict horned figures as gods. This played a part in the ease of the Qun's annexation of Par Vollen. The pyramids also match up perfectly to Elgar'nan's constellation, apparently.
Over in Scuttlebutt, this combined with the 'Those Across the Sea' references and Iron Bull's comments on the kossith have led some to believe that a kossith invasion will be the plot of DA4. And that Elgar'nan will be involved.
Thoughts?
Tin foil hat theories?
Which stage are we on at the moment? 
Ugh, The Qunari and the Kossith are a huge gaping hole of "no idea" in my theories. I suspect they're an ancient-Tevinter Imperium-era breeding attempt to bolster the inherent Will (blood song volume) of sacrificial slaves by mixing elven and dragon blood, but that's not based on much more than an offhand comment by Corypheus that they were "a mistake" and that making the attempt seems like a logical move for Tevinter that would have blown up in their face.
Brutally strong, iron-willed dragon-slaves? Yeah. Nobody saw how that could have gone wrong.
Anyway. Strongly suggestive, but not definitive. We do know that magisters that pushed the envelope (so to speak) didn't like to do it anywhere near the heart of the Imperium itself. It would make sense, then, that if this were an ancient experiment that backfired in rebellion, that the Qunari started a good distance away from the parts of Thedas we're familiar with.
As for the Pyramids and ancient humans, and exactly what went on there... *utterly baffled shrug* I suspect there was extensive dream manipulation involved both in building the Qun and preparing these ancient humans for the idea of willing subjugation to Order, but more than that is pure speculation.
Where do you get your sources? Does Sten reference Kossith at all in DAO, or is it all Iron Bull dialog?