User blog comment:FairyRaven/Fairy Tail Chapter 328: Zodiac, Review and Commentary/@comment-15267891-20130420234919/@comment-7418318-20130421070512

I still think the demon part will be fulfilled by Zeref joining in and bringing some of his demons along, wether they be 400 year old ones that lay dormant somewhere or new creations.

That's probably also the point at which Igneel, Grandeeney and Metallicana will join the fray to counter them.