One of my friends in one of my BFG groups came up with an interesting fluff idea around the Eldar Technology....
Eldar holofields, he reasons, are a *by product* of their drive systems. The reason that they cannot have true "shielding" is that to do so would reduce/obstruct the radiant energy of the sun hitting their solar sails--thus rendering them unable to move. So, it's all tied together. They get the neat moves because they have solar sails, they cannot have shields because it removes their ability to move and holofields are a natural by product of their sails (harder to detect because they are passive systems that have little or no emissions).
Since Eldar technology is BETTER than everyone else's, we reasoned that they are CAPABLE of building ships which have shielding and use plasma drives--but why would they? Therefore, in their merchant fleets, or even in some pirate bands--it wouldn't be inconceivable to find older, less technologically advanced devices. Transports that have shielding, Escorts that might function like slightly better Imperial Firestorms or Chaos Idolators, etc. (but, since they are lacking in the "advanced tech", they use normal rules and not Eldarish rules).
We haven't tried any of these ideas (mixing technologies) yet--but our campaign is developing to do so.
My interest is in the Dark Eldar. I figure that since they are not based on Craftworlds, they would probably be lacking in much of the "advanced tech" of the typical Eldar and would operate a larger percentage of more "normal" vessels--or perhaps even ships that are "cross-tech" variants. Something with the stats of an Eclipse, perhaps--but with 2 shields and only a 30cm move which works only in the Movement Phase...
Though, I'm afraid this takes them too far out of the "Eldarish" camp...