This is the call of the paladin: to protect the weak, to bring justice to the unjust, and to vanquish evil from the darkest corners of the world. These holy warriors are equipped with plate armor so they can confront the toughest of foes, and the blessing of the Light allows them to heal wounds and, in some cases, even restore life to the dead.
Straight from the WoW website.
Paladins are holy warriors who use the light. A "void themed" paladin would A) break the lore of the class, and B) be an entirely different class altogether.. as paladins are a class specifically defined by their "holy" warrior theme. The void fits no where in the paladin class fantasy. A void knight would be an entirely different class. Let's not ruin the lore of well established classes simply because of "muh void elf paladin"