I kind of doubt it'll be a WoL doppelganger since they already did that in the Dark Knight quests, though it's possible. As far as I know Square has said that Derplander is his own character, which would presumably mean he's the Warrior of Darkness.

Elidibus explicitly said there were more WoDs than him, though. At least one person's suggested that they could be the MIA Scions, which I have... mixed feelings on.