Hmm. Okay. I prefer the skirt myself (you can draw Supergirl with a skirt and not make it exploitative. Having it longer than it currently is is a good start), but I can live with this. Especially compared to some of the outfits she's sported over the years. ying_ko_4 is a longtime DC nut, I'm quite sure he can back me up on this.
And there's the cynical view - so now artists can draw Supergirl's ass without the skirt getting in the way. Yay feminism!