I'm craving for Giruvegan and the Grat Crystal. Imagine a set of various teleporters, random rooms, no map and 24 people left in there. I'm pretty sure some woul dget lost for ever
As for the bosses, I don't know FF Tactics so I can't say, but I loved FFXII's Ultima and Zalera. But the death theme is kinda already in Mhach, so why not Shemazai, Zeromus or Exodus (with tilting platforms so you can fall to your death)

Nabudis could be interesting too, it fits the ruin-mood we see in the Orbonne pictures.