I like the idea of the list! Sounds like no matter what you do with list, you're almost guaranteed to have fun with it.
I'm thinking straight Dark Eldar are the way to go. The Farseer would be nice, but not necessary. Paint your Archon or Succubus (if you include one) in the colours of the army and it should look fine. Better yet, use a spare Harlequin model as a Succubus just to keep the theme of the army.
Will you be using Raiders/Venoms for your Wyches? It's really hard to keep them alive otherwise, I'm sure you know that. It may not fit with the theme of the army as well to include the transports, but it's better than losing your troops at the end of turn 1.
Maybe a Haemonculus Coven list would work, with Wyches and Harlequins thrown in. That would cover everything, except for the Eldar if you really want to include them.
Why do we ride atop these elegant craft? The better to hear the screams of our prey as we ride them down, to savour the fear etched on their faces, to taste the tantalising tang of their blood in the air as an appetiser before the feast. But most of all we ride them so that the slaughter may begin as soon as possible.