I wondered after this too. I think that Eorzea will be a realm very soon that will literally have more Primals than Elements. We have two named Elder Primals, Bahamut and Odin. Then there is Fenrir, where does he fit in?

Maybe Bahamut is an Elder "Fire" Primal from Allag, a "ghost," that is not elementally locked, without living worshipers. Perhaps Odin is a formerly elemental "ghost" as well. My guess is Fenrir and a bevy of others will pop up from Final Fantasy archetypes.

My theory is that they really are heinotheistic beings. Heinotheism is a system that is really foreign to moderns but was pretty common in the ancient world. Basically, gods were seen as regional. There would be an ancient Mesopotamian god or system of gods, an Assyrian pantheon or singular Baal, a singluar Hebrew God, and so on. For many of the people these gods were almost like divine barons, each ruling their own little barony or dukedom. A wandering Assyrian might head into another region and he would still worship his god as his own, acknowledging the existence of others, but not the primacy of them over their particular region.

I think the Primals would be similar, there could be a fire Primal of the ancient world, Bahamut who is now faded (although still intensely powerful, well beyond even the modern Primal over Eorzea). There there is Ifrit, he is the localized Primal of fire for Eorzea centered in the worship of the Amal'ja. Meanwhile in Othard, there is Salamander, Phoenix or Maduin as the localized fire Primal summoned by dragon men or something. Perhaps in the centuries gone Ilsabard had a fire Primal of its own, Belias. They seem to be intensely jealous beings, with no particular concern for the elemental nature of any of the others, simply that they have worship.

Secondarily, I've wondered if there could be reduplication of elements even regionally like the Twelve have doubles of elements Astral and Umbral; Astral Fire and Umbral Fire.