I did find some beautiful and very Steampunk compatible long skirts today--but not necessarily for summer. All are considered "evening" or "formal"--which does not necessarily mean a clever Steampunk could not successfully work them into a lovely and even practical everyday look, but which does mean she will have to take them to the dry cleaners.
Skirt by Marissa Baratelli, found here
Oh, isn't that gorgeous? Reminds me of a parachute silk wedding dress I saw in a museum, which a bride made from the chute that saved her fiancee's life during WWI. It has a slight industrial feel, so it is pseudo-Steampunky, elegant and modern all at the same time.
By Talbots, found here
The lovely lacy detail on this second skirt is hard to see in this photo, but there are more if you follow the link.
By Calvin Klein, found here
If this is not a stiff, rustly satin, I could see it easily paired in the daytime with a white cotton/linen blouse, something with a faint Victorian feel, maybe a bit sheer with a white cotton camisole hinting through. . . . Too bad the listing does not actually give the fabric content.
By Ann Taylor, found here
Look at the beautiful period-appropriate detail at the hem. Lovely. Too bad the skirt is 100% non-period-appropriate polyester. A really high quality synthetic might look and move enough like satin to still be beautiful, but no way to tell from photos. Still, it is a skirt with clear steampunk potential.
By Laundry, found here
Another gorgeous faux-satin. But again, the fabric is acetate, which is usually fairly stiff, and might give off that terrible skree, skree, skree synthetic swish as you walk. The look is beautiful, though.
At least today's looking inspired me to consider "evening" skirts as day wear. Tell me if you are inspired too!