The Mogstation items that can be placed in the Armoire are all previous event items that have been previously coded to be Armoire-storable before they were available on the cash shop. They did expand the Armoire slightly this patch to include the Fan Fest items (Tidus/Yuna outfit and Moogle Outfit), Maid Outfit, Butler Outfit, and the Far Eastern Journey set (Amazon promo). I do agree that it should extend to all cash shop purchases, however.

I would not recommend storing Mogstation purchases in the Glamour Dresser though, as once stored, they cannot be removed without destroying the item. Best to keep those in a retainer if you can.