"An army may not have a duplicate of any Detachment.
Note: This includes “Decurion Style” Detachments which are comprised of multiple data slates and Formations. They may not take duplicate Formations within the Detachment, although they make take duplicate Data Slate units within the Detachment if permitted to do so."
I hope they give an exception to the "aspect host" part of the Eldar decurion. It is the only way to get asepct warriors into the decurion and you only get 3 squads per formation. It is meant to be able to be taken multiple times...
Are Eldar just going to be limited to a maximum of 3 Aspect Warrior Squads? I was actually looking forward to playing a footdar army with all the different aspects, but now it looks almost impossible to do under their rules. Man they make it really hard to do anything fun...