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Have a firmer date on the build (or "build", if it really is just a distro cart) and, perhaps more interesting, a localization spreadsheet!
XY had a worldwide release, so there could be a few fun stray ends in there.
You'd have to hack into the main game for that. If it has nothing "behind" it in the released game, it likely never had anything. It feel like GF was thinking of maybe doing what they wanted to with the Gen IV Legendaries by having in-game locations you needed a Key Item to access that'll be given away via an Event. That empty crystal room with the light shining down in Reflection Cave (where you find the Alakazite later on) was meant for Diancie, the Chamber of Emptiness was meant for Hoopa, and finally the locked Power Plant room would have been for Volcanion. But unlike the Gen IV Event Items which got as far as being programmed in, they decided against the idea. And while the room in Reflection Cave & Chamber of Emptiness was accessible, they just kept the Power Plant door locked. If they finished the room it would be in the main game, if it's not then they never got that far before scrapping the idea.