I'm still holding up hope for the Necromancer angle, especially if it turns out to be another Tactics Ogre reference. Going WAY out of the left field, it could lead to teases that the Necromancer job (don't look at me like that, it appeared in the FFV remake) would use scythes.
Back to the point, while I wouldn't discard the Lambs of Dalamud, they dabbled more into Voidsent while PotD is more into undead, reinforcing either the Necromancy or Ascian angle. However, I think there's little chance of us finding either Ysayle or Haurchefant. From a story point of view, their deaths were already used for emotional value and milking it further would probably not have the desired effect
(not to mention we've already seen their "spirits" in the MSQ, real or not, it's unlikely they got "spirited away" into floors 51+ so soon)