CitarOkay guys, it's painfull to say that, but I just get my withedwarf and... Biel'Tan is apparently completely destroyed. Here's the quote translated from french :
" At last, it need a major cataclysm - the destruction of Biel'Tan and the death of many of his inhabitants - for the Eldars to accept the possibility that Yvraine is right. "
So in the book, we will follow Yvraine (who's not Malys...) in her journey to unite the Eldars (Craftworld and Corsairs and Harlies and Dark Eldars) in her project to awaken Ynnead as soon as possible.
There is a "new faction" called the Ynnari who unite all eldars (so probably a "castellan of Imperium" detachment).
For the matter, the "Aeldari" is apparenty the name of the ancients eldars, before the Fall. In the very end of the 41th millenium, we're still "Eldars"
The WD tell us that the book will have some formations (a small photo show one with Incubi and I think some dire Avengers), a new psychic discipline (the Revenant), relics and such others things like that.
For the rules, it is confirmed that the Ynnari Triumvirat (Yvraine, The Visarch and the Yncarne) are buffed by the death of "nearby units" (so, friends and foe ?). Yvraine is a psyker, and the Visarch is "over the top of all other eldars caracthers in close combat". For the Yncarne, they said that He/She will be VERY VERY HARD to kill, and that the death of nerby units will reinforce that fact. So, healing ? FNP ?
It's all I can say at the moment, I didn't read all the WD so... stay tuned !

CitarFor all we k now yet from the WD, Vect disagree with the Yvraine's project of unity and Ynnead awakening. The Covens too, because "dude, necromancy is OUR business !".

CitarYvraine, who was a succubus, is killed by Lelith and reborn as the envoy of Ynnead. This cause a disjonction (seriously, again ? xD) and open the Khaine's gate.

CitarEldrad is judged on Ulthwe by a concil of farseer for he have tried to awaken Ynnead by himself and without their approval. His judgment is interrupt by the arrival of Yvraine, and then the arrival of some eldar from Altansar (but we don't know at the moment what they'll do).
For Biel'Tan, this is the wreck of his wraithbone core and the death of his inhabitants that partially awake Ynnead.

CitarFor the Vysarch, it is said that he his some sort of bodyguard (and "more", but it don't said what), that he wear and armor of the ancient eldar beforme the Fall, and that he is a "dead eldar hero resurcted". Did I say that "somebody" died on Iyvanden ?

On Iyanden "a great hero died while fighting against the chaos forces, but death isn't definitive now...".
So, the Visarch IS Yriel.

CitarIyanden is attacked by a chaos fleet when Yvraine arrive on board. Iyanden is the last step of her journey, then they'll go on Klaisus meet the survivors of Cadia.