When you pre-order Heavensward, this is where you enter the code https://preorder.eu.finalfantasyxiv.com/en
it will give you a code for the PS4, although it can't be entered yet, but they'll email you the code.
Yeah, they're adding Final Coil to the DF and removing the loot limit from WoD which is a surprise as I didn't think that would happen until Heavensward.