They might add new summon spells (IV+), but what role would they fill? There's already a lot of overlap between Ifrit & Garuda.

I believe the next 2 primals we're supposed to fight are Shiva & Ramuh. The cheap and easy way out for them might be to just replace Ifrit, Garuda & Titan with Shiva, Ramuh & Leviathan in the same way that the current egi's replaced Carbuncle.