Personally, taking inspiration from the way British Officers lead native commonwealth armies, I'd consider a single farseer protected by a bunch of Pathfinders escorts overseeing a "main detachment" of Ork mercenaries or "liberated" human soldiers extremly fluffy.
Now, ruleswise, I'd claim that the current codex is pretty weak with a few strong entries. I think if you intend to play competively, you're better off with just the shiny pieces of the Eldar codex as the frosting on your Imp, Marine, Ork or Necron (I know, I know...) cake.
Questionable how reliable that info is, but it's the best we got right now.
For instance, I kept playing foot'dar all through mech-friendly 5th. That has to count for something. But then again, I do have a reputation in my (casual) gaming group for all kinds of nastiness. Again, effective play plus style equals bragging rights.