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So, my idea on how this gets handled is that the plateau is the battle facility, considering how generally small it is I have a feeling that it will at most have one to three facilities best case scenario. The lack of transfer mons in the base game is because there won't be anything besides the chimera paradox added by the first expansion.
The SECOND expansion will alow you to access at least part of kalos, being on the other side of the battle facilities and will thus be a separate map, making an increase in the existing town map unnecessary, and allowing for some degree of reasoning behind kalos not being plainly visible from paldea.
But considering how slack ass gamefreak is it'll probably just be a port of crown tundra.