well, harlequins are the webway wardens and also have ties with the black library. So maybe build some kind of webway junction? Harlquins are also unaffected or at least less affected by Slaanesh, who usually messes with the eldar psyche when close by. So you could build a harlequin group leading an expedition to a crone world to hunt for the Tears of Isha (waystones for the CWE). For that you could build palace structures and have a nice diorama scene where your Solitaire (archon) fights a greater daemon of Slaanesh?