Since the release of the Eldar codex, there has been a big question on what to do with the Iyanden supplement. Of course it was one of my favorite eldar releases, and many people in the hobby had hoped that this trend would continue. However, with lack of support for the Iyanden supplement, it looks like its on its last breath, and does not speak well for other existing codex supplements.
So customer service finally responded to questions on exactly what we are to do with this book. Of course the answers were most likely not what we wanted.
via a reader here on Faeit 212
apologies for the delay in replying I have been waiting for a answer from our games designers.
The Supplement Ilyanden was meant to go with the Older Eldar Codex and thus was not really designed for the new codex.
However feel free to adapt the rules if you wish in order to keep using it in games.