Some wild speculation about a certain macguffin from 7.0

[mallleable]

Some reiteration, we know that The Dimensional Key is capable of dimensional travel when it allowed the Milalla to flee through a portal from The Source to The Ninth. It is also capable of dimensional fusion, allowing The Golden Gate, and The Dome to fuse to The Source. So it might be the case that The Key is simply capable of dimensional manipulation magicks, so it could be possible to use it to do the opposite of fusion, dimensional splitting -- or sundering.

I think Venat could have used the crystal within The Key to sunder the world. This could explain a couple of things like why Azem's sigil appeared on it as well as give Calyx, and Preservation the detailed knowledge about the shard system. Venat's memories of the sundering could have been seared onto the crystal, and Preservation could have found them when they made The Key. Which leaves a couple of possibilities: Venat made the crystal to sunder the world or she repurposed the crystal. I'm unsure she made it because otherwise there would be 'Venat magic' on it, not 'Azem Magic.' It also seems a bit odd to include other spells on it like dimensional travel, and fusion when designing a thing to sunder the world. So the possibility that she simply repurposed it remains.

I still think it might be some kind of Auracite that contains a dimensional fusion spell (like how the Auracite within the Heart of Sabik contains Ultima), and Venat crossed paths with it during her time as Azem and put a protective ward on it to mitigate its corruption, and would later repurpose it to sunder the world. I think we should go to Elpis, and pay Ventat another visit.

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.

[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.