User blog comment:Omega natsu2/Chapter 390: The Story of a Boy, Predictions./@comment-5873677-20140621142042/@comment-24039250-20140622015143

Yeah but that was based on F-Rogue's timeline, not by the current timeline, so no one truly knows when it will happen. Knowing Hiro Mashima though it will happen, either sometime soon (this arc) or later (next arc).