Obviously, I'd like to see Eldar ships sometime, but I know its unlikely given the tech they use:
Wraithbone, Solar Sails, Bright Lances, Shuriken cannons, Distortion fields (holo shields) and Mimic engines (give friendly energy signature when out of visual range).
The weapons shouldn't be too hard to make, more powerful lance, faster-firing flechette cannons that do shield damage too, Eldar Torpedoes should be similar, with a little more penetration. Wraithbone is simply too. The Holo Shields might be possible eventually as Walt has made cloaking a planned feature. But I don't think he has Electronic Warfare planned at all, which is a shame as Mimic engines and general ECM are important for Eldar ships.
I've had an idea for solar sails though, a light cheap armour piece that adds a small just a little thrust in all directions. Long pieces could have a little more thrust along the long edge, making it preferable to build up long lengths of sail structure for maximum efficiency. This would certainly give Eldar ships their fragile manoeuvrability but without cloaking too I'm not sure if it's worth it.
Structure parts are extremely hard to hit with most weapons. I wonder if there's a part of the structure code that can be added to every Eldar part, to make them all hard to hit.