Patch 6.5/6.55 speculation based on the art work.

[Enkidoh]

Cracking out the list of FFIV bosses, here are the ones that we haven't somehow seen in XIV, in alphabetical order.

[*]Dark Bahamut

We did get 'Lunar Bahamut' as the final boss of Pagl'than back in 5.5 though, so that sort of counts.

[*]The King and Queen of Eblan

Well, to be fair Eblan is the apparent original name of the area where the Garlean capital is located (the area around Camp Broken Glass is called the 'Eblan Rime' on the map, and some of the enemies there also have 'Eblan' in their name). Interestingly Doctor Lugae did appear in the Tower of Babil though, so... maybe they might show up too as Garlean nobility turned into Blasphemies (or else were more fittingly more of Lugae's twisted abominiations?). Or voidsent even.