The term "world line" is still a bit vague as far as what it truly defines.
Given what we know I think that it makes most sense for it to mean from a data world line to the RoL world line. It is still unclear what the device Maleficent has found truly is. Seeing as how Lauriam is also there it most likely exists in the data world, meaning that machine might be a way to escape the data worlds. However Darkness has described the ark to be in the castle which is supposed to be a way into the future. In which case this device may be accomplishing both methods. Regardless, the Five will find a way out of the Data Cage, and at least three characters will jump into the future.
What I am currently thinking is that the five who jump out of this cage and into the future are going to be Lauriam, Elrena, Skuld, Ventus, and Brain. Ephemer stays behind and remains trapped in the Data Cage along with the rest of the uber powerful Dandelions. (I also feel like this Data Cage is what the Black Box contains). This could possibly explain why he appears before Sora during the Keyblade War alongside a whole bunch of Keyblades. As for the other five, I definitely feel like something will go awry with the machine causing it to malfunction and scatter them across space and time. Brain will be the first to emerge, and be the one to establish the new order of Keyblade wielders who will build Scala from the ruins of Daybreak, with the main goal of being to protect the light. I also feel like Brain will be the one to receive No Name which would make sense for the way we know history will unfold. Then later on the other four emerge, scattered across the real worlds, with no memory of their past lives. Skuld lands in Radiant Garden, where she becomes Subject X. Lauriam and Elrena are unknown, but emerge presumably together and stick together until becoming members of the Organization. Ventus emerges in a place where he is quickly found by Master Xehanort, perhaps Scala?
Hopefully Dark Road will expand on the World of Scala.
