With the Expansion coming soon, i'd love to see the Soul Crystal system used for Hero classes:

Tanks:
Cloud
Lightning
Warrior of Light
Cecil
Auron
Paine
Ashe
Onion Knight

DPS:
Squall
Kain
Tidus
Luneth
Bartz
Tifa
Zidane
Rikku
Vaan
Snow
Noctis

Healer/Mage:
Terra
Yuna
Layle

I'd love to see something like this make more use of the Soul Crystal system.