User blog comment:CNBA3/Operation Face/@comment-24603221-20140605195010/@comment-68.1.178.233-20140606045003

Well Mashima did write in one of the FT volumes that he had, at least, three more episodes left in him. And by episodes, I think he means arcs. This was during the Grand Magic Games, too.

So assuming the sun village arc counts (it was pretty short), then after Tartaros is finished, he might start thinking about how he's gonna go about wrapping it all up. In which case, he'll probably want to keep E.N.D. from being summoned here and save that for the next arc? I don't know, just throwing this out there.