User blog comment:FairyRaven/Fairy Tail Chapter 400: Wings of Hope, Review and Commentary/@comment-18654001-20140913113607/@comment-4829046-20140913115505

Zeref didn't really have an inclination to explain too much, plus I'm sure he didn't follow up on everything Acnologia did. So the possibility is still there. Nothing is concrete yet. And I'm not insistent on it, just think it will be a nice development. :D I like the concept of turning into a complete beast out of one's lust for power. They had that recently in the movie Brave as well, which is why I mentioned this theory.