The idea is that the power of faith and belief, along with strong emotions like hate and revenge, channeled through the power of crystals, can birth fabrications of gods and god-like beings right? So Primals in theory could be anything, limited only by the imagination of a sentient being or race. We've seen Primals which are gods who are worshipped - like all the beast tribe gods, Primals which are based on historical figures who were real - like Shiva and King Thordan, Primals based on deceased dragons like Bahamut, Primals based on myth alone - like Good King Mog and Shinryu,
So the next thing I'm wondering is... do we think there's an actual requirement that a Primal's subject is actually no longer part of the world? Could a Primal be awakened of a living entity without their consent? What happens if the Warrior of Light is captured some day and everyone thinks we're dead. But we're not. And they all pray for the Warrior of Light to save them from some great calamity and channel all their hopes and dreams into crystals? Would another Warrior of Light be born as a Primal?
For that matter, why does it seem like only one of a single Primal can exist at a time? If there are say, 10 different tribes of a given Beast Tribe, and they are separated but share a common faith, if there are enough crystals for each of them, could there not be say 10 Ifrits in different places at once? What limits this? Each Ifrit isn't any more real than the other, so why would it matter?