You can't form detachments with the aeldari keyword anymore. Not sure how a mixed Drukhari detachment would work if it contained cult, covens and kabal. Obviously they don't get obsessions, but presumably they still get a kabal keyword. I don't know if that opens up the obsidian rose stratagem though or if it needs to be a pure detachment.
Do you fight for the Dark Gods? The Drukhari gave birth to one of them. By partying.