Riveting discussion about Sigmar's penis aside, I wonder if Cathay has any Waystone-related knowledge of their own? They'd be a nightmare to get in touch with, but they have an advanced and unique magical paradigm and cover a large stretch of land at the right latitude for Waystones to have noticeable effects.
Maybe they'd make a good stretch goal for reaching out for Waystone knowledge (though outright involvement in the project might be difficult, given the extraordinary distances involved.)
... A thought: maybe instead of Waystones or Karaks, what they have is The Great Bastion?Depends if they have any waystones. It's certainly not impossible, but I'm unsure the Elves ever expanded into the area, and if they didn't any waystones they'd have would be notably different at best from the ones Mathilde is assembling the expertise to work on.
Maybe that's what their Great Wall does. Perhaps it just collects energy, perhaps it transforms the Winds (again) in some way, perhaps it works as a great big wind-barrier or windmill or something.
Perhaps it's calibrated to turn the Winds into something desirable or useful to Dragons rather than to Elves or Dwarfs. Where the western Dragons are faced with either abstaining from the Winds and sleeping in volcanoes, or embracing the Winds and being transformed, the Eastern Dragons instead did something funky to the northern border of their land, thereby making it easier for them to remain awake or to remain not-Wind-Dragons or something?
... Or maybe it's just a big fortification meant to hold off Chaos, and any anti-magic or anti-Wind properties are just part of anything that is generally useful to put in a fortification.