August 27th 2013 according to the Letter from the Producer XLVI.
Heavensward is already released as of October 2015 for PS3, PS4, Windows, and technically Mac.
Microsoft is not going to let it be on Xbone/360, sorry, they want money.
The VR version of XIV was a proof of concept, its chance of being ported is next to none.
There will likely not be a DX12 version of XIV, the DX11 version is about 10-20% faster if you have a strong card, on a weaker card, use DX9.