The first thought that went into my head when I saw Luka's design was this:
"Woah, she looks totally cool and mysterious and stuff."
Which was then followed by something more bizarre:
"Wait a second, that dress looks totally familiar. Nah, it can't be."
And then I double-checked. And I was like, "maybe the character designer was looking at Wrath of the Lich King artwork right before he had to submit Luka's design for Crypton." So I convinced a friend of mine to make a 4-panel comic about how Luka ended up with the final costume design that you see today:
What I find extremely humorous about this comic is that something very similar happened when Luka's voice actress was put in a similar situation during a Q&A session at Anime Expo.
Also, one other thing I find funny about Luka is that despite her appearance, it seems to be confirmed that she can sound like a ditz.