Hi guys, just a random thought, this is purely theoretical but I think it's something..
What if Dalinar saw at the vision was not just 'Odium's champion' and the 'Unmade' but the Heralds their selves? Think about it...
1. If I remember correctly the vision was supposed to be Honor's version of worst possible outcome. (Correct me on this if I'm wrong) What if Honor's worst nightmare would be the total corruption of his Heralds turned as Odium's other than True Desolation itself?
2. Stormfather didn't actually saw the last part, meaning he is dependent on Dalinar's description, I agree on the first one that would be 'Odium' the golden, terrible light, though I am not sure about the 'Heat' part, this could be important. Then he said 'Nine Shadows', maybe, just maybe SF misinterpreted this knowing that there are 9 Unmade coincidentally thinking it was them but it could also point to the other 9 Heralds that turned their backs on their Oaths. (This one's important)
3. Since the Herald's are not honourable any more (Oath breaking) they could be already being lead by Odium and they didn't even know it.
4. "He saw something terribly familiar in them." What comes to mind about who would be Big O's Champion is someone Dalinar already met, sons, friends, enemies. If memory serves right I think Dalinar and Taln already met (Correct me on this). If not, it's not familiarity of the eyes but the emotion within the eye is what he's seeing, like looking at a madman or something, Taln quite fall under this one too.
5. It is also possible it would be Taln because Honor does know what his Heralds look like right?
I may be just over thinking this though.