Why does everyone assume Zodiark can be summoned, when it's probably a being similar to Hydaelyn and is pretty much the source of aether itself.
If their goal was to summon a special being such as Zodiark (if he's not a crystal), there's faster way to do it (like possessing the different religious leaders to alter the cults, leading to a worship of Zodiark).

The only point in becoming Shiva, for Iceheart, was retaining her will and having the power of a primal. Do you actually think they'd want to give the power of their "One True God" to their sworn opponent, to make them a being able to feed from Aether, and thus giving them the power to actually kill them (just like what Leviathan did to the Sahagin priest).


As for summoning primals, "easy" to think of workarounds.
- Capture the essence of the primal in an auracite (similar to how you'd trap a soul in it),
- Bring an auracite (or a lot), slowly fill it/them over time until there's enough aether to sustain a primal for a certain amount of time.
- Use both the essence you captured along with the aether auracite
- When the aether is depleted, the primal's essence disappear since no more to feed on.
- ???
- profit.