You will be able to use Harlequins in battle-forged armies with a new rule called Travelling Players. It is apparent that this rule or a rule that is similar will be used for the new Corsairs and Ynnari
via WarCom
Neatly sidestepping the constraints of mission packs, this rule allows you to add a Detachment of Harlequins to any Aeldari army, as if a poised Patrol of perilous pierrots had put in an unexpected appearance on the battlefield.
Importantly, including a band of Harlequins in a Travelling Players Detachment will not prevent you from using Battle-forged rules, such as Power From Pain for Drukhari, special secondary objectives, or the new army-wide Asuryani special rules.**
Travelling Players will allow anyone with existing Harlequin armies to supplement them with more straightforward Asuryani or Drukhari forces, it’s easier than ever to find a place in your collection for some of the wildest and most acrobatic miniatures in the Aeldari range.
Harlequins aren’t the only Aeldari who can cross traditional faction borders — keep an eye out for updated Ynnari and all-new Corsairs.