There is probably no direct evidence to this theory, but I will throw the idea into the air...

What if the army that is laying siege to Caemlyn is an army of darkfriends and/or trollocs?

When I read the promotional text for CoT, it reads - "In Andor, Elayne Trakand fights for the Lion Throne that is hers by right, but enemies and Darkfriends surround her, plotting her destruction. If she fails, Andor may fall to the Shadow, and the Dragon Reborn with it".

This struck a chord with me as I remember in the TDR when Egwene was being tested to be an Accepted. One of the arches she steps through brought her to Caemlyn where it was destroyed by Trollocs, Fades and Darkfriends. The three arches are said to be a form of Tela'Aran'Rhiod so this could be a vision of the future... Especially when it say's in the promotional text - "If she fails, Andor may fall to the Shadow, and the Dragon Reborn with it". Remember that in the test, Rand was caught underneath the beam and he begs her to kill him before the Dreadlords and Fades can turn him to the Shadow against his will.

But then you have to say, how did the army get there in the first place. Could they have used the Ways? Did Loial and Karldin close all the Ways?

Or did Dreadlords use gates?