Theory: The Qunari are a mix of Dragon and Elven blood, born from experimentation.
Very little is known about the origins of the Qunari. While many Thedosians only know the horned race to have come from the north, the inhabitants of Par Vollen do not share their history to outsiders. But as new information regarding the Qunari develops post-founding of the Inquisition, new revelations have been made.
Iron Bull is the main instigator of this theory, pointing at the very possibility of Dragon blood combined with the Kossith at a very early state. A rumor from within the Ben-hassrath, it's possible that such a joining occured since the Tamrassians, those responsible in governing the roles within the Qun, are directly involved with the breeding process.
While most Thedosians believe the Qunari came from unknown parts in the north, most do not know their actual origins since they started coming to Thedas and made war with the Tevinter Imperium. Corypheus, the head priest of Dumat and ancient magister that originally breached the Black City, claims that the Qunari were a race that should have never been. While everything within the universe of Dragon Age should be taken with a grain of salt, at the same time, Corypheus lived during a time when Qunari were not the horned beasts known today.
What Kieran says here only seems to confirm, or at least attribute, to Corypheus's claim of the Qunari being an experiment. If it's not their blood, it's possible that whatever the Kossith were at their time, they were infused with another species blood. And if we take what Iron Bull had to say, it's possible that the Qunari were once Kossith who had Dragon blood injected into their veins.
Here comes the theory part, however. The horns give the theory of dragon blood mixed in its strength, as well as the pointed ears, but it's possible that since the Tevinter Imperium were very adamant on experimenting and utilizing the blood of Elves, they may have tried to join their race with Dragon blood. Perhaps a similar effect to what Reavers have, but instead of drinking the blood, joining with it. It's not the first time in Tevinter's history that Elven blood was exploited for human needs. In the "Claws of Dumat" codex entry, what seems to be Corypheus's slave talked at length of the power of Elven blood needed for his greatest feat. Tevinter's history is plagued with its past of blood sacrifices and magic with the use of Elven slaves. It's not far fetched to believe that the magisters of old tested on the Elven blood. But in joining Elven and Dragon blood, did they seek a more sinister purpose?
This leads into another question - what is hiding in Elven blood? From the taint in Darkspawn, to immortality in the Elvhen, each race seems to be hiding unnaturally strong attributes in their lineages. In everyone's blood? The Qunari own blood not of their own. The untainted Elvhen blood holds the key to immortality and greater magic. Even Dwarves are synced with lyrium itself. Humans may be the only simple, yearning blood. But they may have had the greatest involvement in the creation of the Qunari.