I'm going to guess that it won't necessarily be time travel(though it would be fitting, since the pixies and Titania were in XI during Wings of the Goddess), just based on the cinematic dialogue. A forest that's confirmed to be Rak'tika is engulfed in an inferno, and Matoy'shtola says that she'll hold the line until "Our friend," presumably the WoL/WoD, returns. Despite this, the footage we have of Rak'tika is blooming with life and serene to the point that parts remind me of TERA's environments. In the older footage, Derplander is walking aimlessly as just an archer before receiving what seems to be an echo vision of events from 1.0 to 4.57, and his demeanor changes immediately.

My flimsy assumption is that Minifilia will return to the Source and, with her and Matoya, the Scions will have their souls pulled back, with Matoya possibly using her own soul to bolster Y'Shtola. Come 5.0, we cobble together a way to travel to the First(souljacking our counterpart) with the goal of stopping the Flood of Light, which is now leaking to the Source, entrusting the Scions to hold the line until we finish our job.

I'm just guessing at this point. I have to think it's either shard travel or some weird time crap like 8(which would be appropriate, considering they based Gunbreaker on Squall) or even 13-2(string theory, changing the future to correct the past). The problem is that I don't see where the new zones would fit in what is an apocalyptic scenario on both shards.