Well, there are rumors of the Dark Eldar codex getting redone. It is likely that Harleuins will be in the book. The question is, if Harlequins will be in the codex, who will take wytches? This is assuming wytches are the same as they are now and webway portals remain.
They only time I would take wytches would be if Harlequins can't use a webway portal, or if I am using an all Raider Rush army.