Interesting. I always forget to go back to the codex entries after drinking from the well. I think it has been mentioned on the thread before though. I don't remember all the possible interpretations.
I can't help but read the first line and think of darkspawn hunting the Old Gods. The darkspawn 'scurry, witless, soulless. 'This death will be a mercy,' not 'their deaths will be a mercy,' so I'm thinking the merciful death does not reference the 'witless, soulless' ones. If the Old Gods are corrupted, death would be a mercy, or it could be that death frees them from whatever trapped them in the first place. Then there's the line about the earth blossoming with 'their passing' - the end goal of all this.
If I'm interpreting this right, it certainly gives credence to the Old Gods as keys theory. I wonder what the two spheres could be? The two worlds, maybe - The Void and the 'old world' (where Fade and material world were one), or the Fade and the material world now. The imagery of the two spheres could also have something to do with the orb, if it is in fact one of a pair.
So were darkspawn actually created by the elven gods, then? It would be indirect, of course... Elves create Old Gods, Old Gods tempt Magisters, Magisters become first darkspawn. There was that theory going around about Andruil discovering the blight during her hunting expeditions in the Void.
Or I have it all wrong and the 'witless, soulless' workers are something else. Enslaved elves, maybe?
Also, the whole 'earth blooming' thing... Things grow when two worlds overlap. Red lyrium? Imshael, one of the Forgotten Ones from the Void, does call himself the 'gardener.' But red lyrium was found by accident. I wonder if it surfacing sooner than 'planned' is setting things in motion a lot more quickly than expected - hence Solas's sense of urgency.
Ugh... thinking out loud... Sorry it's a mess. I'm likely way off base, or it's all been said before, but more coherently. 
My first thought is that the Pillars of the Earth are the Forgotten Ones/Titans, who are corrupted by the Blight and dwarves/elves are twisted by it into proto-darkspawn. The Creators in their heyday marshal their forces and quarantine the nightmare, but eventually Andruil and Ghilan'nain are infected, and the Pantheon slowly starts to fall into disorder as the gods war amongst themselves and the prison keeps breaking. Mythal is murdered by human upstarts, and things get real bad.
Fen'harel settles affairs.
The 'earth blooming with their passing' definitely points to some sort of Blight related illness. Then again, the Western Approach is still Blighted from the Second Blight, and the Anderfels from most of them. The unsteadiness of Theodosian society doesn't always get across, I think. This is a continent that has faced multiple extinction crises and has lost a lot of livable land, causing them to fight each other even more. It's quite nasty.
Supporting Old Gods as Pillars of the Earth is Solas's outrage at the idea of them being killed. Possibly they can still fulfill their duty even buried. But their Song seems to be untainted, a pure and glorious song, as the Architect wryly notes in The Calling.
EDIT: My sincere apologies for accidentally dropping this off in the 'Smut' portion of the Great Solassian Cycle.