This has likely already been noted, but, I figure I'd drop my two cents on the off chance it hasn't.
Major final coil spoilers below.
So, in the final coil, we learned this interesting little tidbit of knowledge. We also know full well the Ascians seek to push tribes to summon their primals. Lastly, I believe we can safely make the distinction between the Meracydians and the Dravanians. Or rather, what they once were and what they now are. I'll touch on all this later.
First off, an old post by Ferne stated the following.
Not a beast tribe, but beast tribes. Not a god, but gods.Originally Posted by Fernehalwes
Now, Bahamut was one of the Meracydian's first brood. A great and powerful ancestor. Now, the historian Erik in-game has this to say about Midgardsormr.
In a sense Midgardsormr might also be considered the first of a brood. Once a Dragon King.Originally Posted by Erik
....He perished, though. Yet, it seems he is coming back to life. Much like Bahamut did from the fervent prayers of the Meracydians. Now, take a look at the Ascians motives thus far. They've goaded every beast tribe we know of into summoning their primals multiple times, and provided them with ritualistic items to further the potency of their summonings.
Now, Louisoix's staff, Tupsimati. We now know that it was fashioned to channel incredible amounts of aether, which is how he was able to use it in his ritual to summon forth the essences of the twelve. We also know it is similar in design to the horn from 1.0 that was used to supposedly summon primals. In regards to the Final Coil, Louisoix also turned into the primal Phoenix after using Tupsimati to summon the essence in the twelve, though that in itself isn't directly related to the use of the staff itself as far as we know, and rather the sheer amount of aether in the air and the desperate prayers of those fighting on Carteneau below (as well as Louisoix's own personal wishes.)
What if the Ascians want Tupsimati, that they might gift it to the Dravanians who then would use it to help resurrect the keeper of the lake as their new primal?