I don't know if/how this will happen, but I'm gonna go out on a limb and say at some point I bet we're going to see the Garleans accidentally or deliberately summon a primal in connection with their absolute devotion to their Emperor.
Garleans seem to pride themselves on being atheists and not getting into the primal scene. However, we know that Solus is running around causing chaos for shits and giggles. We also know Varis is essentially out to free the world from Ascians by any means necessary. Meanwhile there's precedent in Heavensward where Archbishop Thordan VII was able to harness the devotion and prayers of Ishgardians through the Halonic church to transform himself into a primal.
I suspect either Solus or Varis is going to take a similar tactic, and in so doing both temper a bunch of Garleans AND present a hell of an existential crisis for non-tempered Garleans.
Not to mention give Gaius van Baelsar an aneurysm.
If Solus specifically does this, he's probably going to be both insanely powerful and piss off every possible person in the game from Ascians to Garleans to the Warrior of Light etc. If Varis does this it would still be wild but less weird metaphysics at work.
Dunno if anyone else thinks this could happen or has similar/contrasting theories?