I would like some actual form of customization and I would personally love that customization come from a variety of areas.

1.) Sub jobs: Increases stats based off your secondary job and from the secondary job abilities, currently since there's 5, you can choose 1 out of the 5 job abilities as your cross job skill that will become a dedicated primary job ability for you to use. Either you get an ability to use for your rotation or one of your primary job abilities gets augmented.

Examples.
Dragoon/War. Vit+20/Str+10.
Defiance: Increases your crit rate (when you complete your combos stacks up to 5x)
Inner Beast: 300 potency ability that ignores 25% of the enemies armor
Unchained: You can reposition yourself as you jump into the place where you'll land. (Everyone see's you jump and so do you but you don't actually jump and instead turn into a shadowy figure and move to where you want to land.)
Steel Cyclone: Delivers an attack with a potency of 200 to all nearby enemies.
Infuriate: Increase determination by 15%

Dragoon/BLM. +20int/10pie
Convert: Turns 20% of MP into HP
Freeze or Spineshatter Jump augment (Ring of Frost): Additional: Covers a designated area in ice binding the enemies inside.
Apocatastasis: Increases your resistances to all elements by 20%
Manawall: Manawall animation + stonekins effect
Flare or Dragonfire Dive augment (Ring of Flame): Additional: Leave the ground ablaze, delivering damage with a potency of 30 to enemies that enter the flames.

2.) Ability enhancing materia: Giving materia usefulness. Each type of armor can contribute to a specific type or role of spell/ability (works with cross class and cross job abilities).

3.) Merit System x Talent Tree x New Age 2hr. Instead of making your job branch into different roles, which that wont be the purpose of this talent tree. Instead it will only customize your way of play. Yet to activate these abilities you build a gauge like previous Final Fantasy games. Your progress resets when you change zones.

You're not restricted to customizing 1 ability. You can customize a certain amount of abilities and give them effects. Yet when you active the one that suits your style of play your are restricted to the choices you make within that time period.

Trance: Empowers the next 3 set of class abilities slightly.
Overdrive: Empowers 1 of your primary job abilities drastically.
Quickening: Create your own combo and effect. Class to Job skill finisher.