Ah, the Eldar. Fine psykers, skilled warriors with powerful weaponry, fancy energy fields and hovertanks. What kind of counts-as army could work well with their rules?
How about a remnant human splinter from the Dark Age of Technology, or a historical force representing a force from the late DAoT/early Age of Strife? There are plenty of pre-Heresy armies floating around, why not some pre-pre-Heresy ones?
The army can have regular troopers (Guardians and derivatives), enhanced warriors (aspect warriors, representing the kind of genetic engineering that eventually led to space marines), lots of high-tech devices and emerging psykers.
Battle Leader (Autarch)
-Skilled enhanced warrior, variety of high-tech gear and weaponry available.
-various powers, witchblades as proto-force weapons.
Enhanced Warriors (Striking Scorpions, Fire Dragons, Howling Banshees)
-Various specialist squads depending on weaponry.
Men of Stone (Wraithguard)
-Artificial humanoids toting mini vortex launchers.
Troopers (Guardians, Storm Guardians, Guardian Jetbikes)
-Soldiers with early versions of what eventually become bolters along with crew-served weapons, and assault/bike versions.
Enhanced Warriors (Dire Avengers)
-Armed with better versions of the prototype bolters, better armor, access to some other weapons/tech.
-Back when cameleoline was fresh and new.
Enhanced Warriors (Warp Spiders, Swooping Hawks, Shining Spears)
-More enhanced warriors with various specialist gear.
Light Hovertank (Vyper)
War Wheels (War Walkers)
-Same role, heavy weapons on big spinning wheel instead of legs.
Enhanced Warriors (Dark Reapers)
Hovertanks (Falcon, Fire Prism)
Men of Iron (Wraithlord)
Vortex Launchers (D-cannon support weapons)
Not really that big a departure from regular Eldar, but could be fun for a modeller to create pre-Imperial versions of various things.