In addition to the Embersilk Gown, a number of other tailor-made cosmetic-only dresses are also restricted to cloth for some reason, which is unfortunate considering many of the other “casual” items had their armor restrictions removed entirely (like many of the grey/white cloth hats and the Haliscan clothing being full cosmetic now).
While we’re on the topic, there’s also another was-always-purely-cosmetic vendor robe for consideration: