I'm kind of hoping they eventually elaborate more deeply on the metaphysics of soul including exactly what it is that makes Echo bearers special and by extension the Ancients.

I'm also rather curious about exactly what it takes to completely extinguish a soul, considering that "shattering" an Ascian's soul does not entail destroying it entirely but simply compromising its integrity to the point where they can no longer resist the Lifestream's pull. Completely draining someone's incorporeal aether is also implied to not be sufficient to destroy the soul and that there's some deeper, more durable aspect (Perhaps the part that has a "color" that only can be perceived by those with an exceptionally keen manifestation of the Echo) that can survive virtually any form of death; with Endwalker being the first time it's been explicitly stated that they can be removed from the cycle entirely through extreme circumstances.