Although we saw the ruler of Nifelheim and Izunia, as well as Aranea, I think there could be one more, final true villain that SE are keeping until we play the game for ourselves. Imagine fighting the guys I just named as end game or close to end game bosses? They don't seem that intimidating or scary.
A couple of months ago, i remember SE saying that the villain for FFXV would top all the previous villains (http://www.cinemablend.com/games/Final-Fantasy-XV-Villain-Top-All-Other-Final-Fantasy-Villains-76607.html)
Although we saw the ruler of Nifelheim and Izunia, as well as Aranea, I think there could be one more, final true villain that SE are keeping until we play the game for ourselves. Imagine fighting the guys I just named as end game or close to end game bosses? They don't seem that intimidating or scary.