We didn't really "solve" primals, we just got better informed about them. They still need large amounts of aether to manifest and still need to be maintained with aether, absorbing it from the environment. That doesn't mean that those not-in-the-know won't continue to summon them, though. Honestly, from what we've seen ascians aren't even really needed to teach summoning as long as the requisite factors exist.

Back to topic: I would love a fat chocobo primal, even if it is relegated to Hilde. It could be very fun with very unique mechanics.