The thing is, the first two times it happened were meant to coincide with, and advertise, launch of the Lightning Strikes game. If I'm correct, the JP and NA launches. The third time was as part of a month long first anniversary celebration for ARR where they brought back several one-time promotional events for an encore. So it's not likely that they have any plans to bring it back, though I guess they probably could if SE ever chose to do more with the FFXIII storyline.