Welcome to Librarium Online!
Just wondering, would it be fluffily possible to do craftworld Eldar that have since returned to their old ways? Because I'e got some real nice conversions for it. If so, do you think they could be represented as an allied eldar/dark eldar army (despite this not being legal normally). Flufffwise they'd just be the one force of course.
Yes, there are some CWE who leave the Craftworlds (and become Corsairs) and then turn to their true nature.
However, I'm not sure if an allied Eldar force could represent some CWE defectors. Any CWE who turned to the DE would've long since abandoned the path, ruling out Aspects, Warlocks, and Farseers. Additionally, it's doubtful that Wraith-troops and the Avatar would be around for long with the DE.
I was thinking more about Falcons, actually...