Nice find Kangaxx! It fits perfectly with my idea about the Tevinter Imperium and Flemeth/Morrigan:
The Tevinter Imperium once was the most powerful in Thedas. The leaders were Magisters with the Imperial Archon at the top of the hierachy. They worshipped dragons - the Old Gods (Codex #132 "The Old Gods"). Those in return teached the Magisters magic in the first place - blood magic beeing part of it (Codex entries from Brother Genitivi's "Tales of the Destruction of Thedas". 4 parts, starting at #211. Most interesting!).
At some point, the Magisters opened a portal to the Golden City at the heart of the Fade to take over the throne of the Maker. They failed and were "kicked out" again, but tainting the Golden City along the way - now known as the Black City. The Chantry tells that the Magisters then turned into the first darkspawn, but maybe not all of them? (hint: Flemeth). Codex #212, Brother Genitivi again: The Old Gods were then imprisioned by the Maker, now in deep slumber. The Magisters, now darkspawn, seeked out the Old Gods in the Deep Roads. When they found the first, they corrupted it with their darkspawn taint, turning it into the first Archdeamon. The first Blight was born.
Fast forward a few centuries... another Blight (the time the game takes place). You learn that the essence of the Old God within the Archdeamon needs to be extracted. That's the only way to end the Blight. For that, another tainted vessel has to be present. Either a Gray Warden represents that, thereby destroying her/himself along with the essence. Or, as Flemeth's daughter tells you, an unborn baby with the taint. The difference is that the essence will be preserved in the latter case, but cleansed from the taint. The Old God will be what it once was and live on as the soul of the child.
Isn't that the ultimate goal an uncorrupted Magister strives for? If you talk to Morrigan as she comes up with the ritual, she tells you that this is the very reason that she came along in the first place. That baby was the plan of her and her mother all along, the essence is the only thing they care about. If you ask about the ritual, she says its blood magic - first known to the powerful Tevinter magisters, taught by the Old Gods themselves.
It all points to the old Tevinter magisters seeking their Old Gods. They had everything, but lost so much. I wouldn't blame them for fighting for what they once had. And somehow I think Flemeth fits pretty good in that picture
Then again, I'm not sure who or what Flemeth really is supposed to be. Maybe she's the Imperial Archon, travelling from one body to another to survive over centuries? All (or most) of her fellow magisters are tainted, eventually discovering another Old God and ultimately feeding it to the Wardens to kill. This is already the fifth Blight, and there are only seven (Codex #132 again). Maybe she tries another approach with the baby this Blight, playing the Wardens. Or maybe she's Dumat, the Old God of the first Blight. You need blood of an Archdeamon for the Joining to become a Grey Warden in the first place. Which means that the essence of that God could not be destroyed (at least in the first Blight). While codex #213 mentions that the Gray Wardens were born during the first Blight, they just couldn't be Wardens with the taint as we know them from the game. But well, they had griffons.
Oh my, so many unanswered questions...