An army list as in what units are IN the craftworld? The craftworld has ALL units (DE / Eldar / Harli / Exo)... if you're asking about HOW to field such an army... now, that's up to all of us to figure out...
The BEST answer would be for GW to liberalize ally rules. Then, one army list could "slot in" other units. There is precedent for this--the Kroot working for the Tau, or the Chapter approved Human militia units under Tau hegemony. Unfortunately, GW isn't likely to be that accomodating...
That being taken away from us, I see two options:
(a) A LARGE force, 3500-4000 points, which has to be deployed in "detachments". Each separate detachment could deploy in anr around each other to give the impression of a large single CWEO army.
(b) For official Rogue Trader/Grand Tournament play, another approach seems called for... and Agis Neugebauer, in his Dark Harlequins webpage
http://www.agisn.de/html/dark_harlequins.html
may have pointed out the answer. Pick a predominant army list... let's say CE.. and use figures from the other branches of the Eldar as "proxy" for the units IN that CE list. For example, Dark Eldar warrior figures could be deployed (in CWEO colors) as troops choices, proxying Guardians, and using the Guardian specs (including weapons). Wyches could be used to proxy Banshees... and so on.
Exodites could be proxies, most belike, by Warhammer Wood Elves units, perhaps with fusils/"rifles", being used in the Rangers category, for example...
Using GW figures would make the army RT legal... using them as proxies, deployed as a standard army, sidesteps the "allies" issue... and the board would have an army which LOOKED like a mixed-brethren CWEO army.
Comments, analysis, refinements?