it's probably just some vanity set they threw in for ppl that go: buhu no THF /rage.
"In anticipation of new features planned for patch 2.4, an extra slot has been added to the soul crystal section of the Armoury Chest."
Duno if this means NIN, but there's TWO open slots...so there was room for NIN stone, already...so maybe they will surprise-add THF