I think that's my hang-up, too. Everybody in a skirt. If the society wears robes, like Greeks or Romans, I go with 'everybody whirling in their robes, long or short.' Even in traditional Scottish dancing, where the men wear kilts, I believe the women don't, and wear longer dresses.
"It was a full-on square dance, or some such, people whirling, every gender imaginable in fluttering skirts."
Is it meant to be an actual square-dance, with stereotypical
overtones of cowboy hats, boots and hooting-and-hollering? It's kind of specific, which may or may not be what you want. Perhaps 'country-dance' or 'round-dance' would give the vagueness you want?
I think if this was part way through your story, you have other chances to introduce clothing styles, while if it's one of the first lines, you might want a little more description.