I always joke about how the Ninjutsu is going to have the primals come down and assist and be more like Summoners than the actual summoners. But I was thinking, you know how in the old games the summoners would disappear after summoning with orbs floating off and bringing down the summon. Why not give the summoners four commands like the ninja. It'd be Body, Mind, Soul, Evoke. And based on the order you'd get your summon.

Ifrit - AoE fire damage and burn status that lowers attack and a DoT
Titan - Linear Earth damage and defense boost to the party.
Garuda - AoE wind around the caster and group haste
Ramuh - Conal lightning damage and magical defense boost
Leviathan - Linear water damage and lowers magic defense
Shiva - Sweeping Ice AoE and lowers physical defense

And King Mog would be the fail and it does a random effect to both sides.