Some wild speculation about a certain macguffin from 7.0

[Cleretic]

Its sundering capabilities could also explain the weird pocket dimensions that are present like The Strayborough Deadwalk, and the space that would become Sareel Ja's Vana'diel. They could have been created when Preservation started experimenting on the crystal.

Sareel Ja's Vana'diel isn't a pocket dimension, it's a holodeck. That holodeck's exact location isn't clear, but it's by all evidence somewhere near Yak T'el, he made it out of electrope in/around the Skydeep Cenote. There is the matter of the Vana'diel that he saw when he went through the portal, but that seems to be Actual FFXI Vana'diel, which was known.

[mallleable]

Sareel Ja's Vana'diel isn't a pocket dimension, it's a holodeck. That holodeck's exact location isn't clear, but it's by all evidence somewhere near Yak T'el, he made it out of electrope in/around the Skydeep Cenote. There is the matter of the Vana'diel that he saw when he went through the portal, but that seems to be Actual FFXI Vana'diel, which was known.

"Fortunate, then, that that world between worlds was filled with structures made from electrope. More than I could ever hope for."

You're probably right about it not being a weird pocket dimension created by potential localized sundering, it's still a bit unclear but it seems like there is a lot of electrope floating around in the rift around The Gate's fusion point.