I'm going to copy/pasta my comment from our discussion on BG about advanced classes. Advance class growth can be done within the current construct of the armory system (weapon = class).

Yes. They can actually keep the current action/trait system that's in place and just apply the rulesets already in-game for various abilities. For example (just picking random numbers here to illustrate point):

Advanced Class: Black Mage (R25)
Total Action Points Available: 30
Spells I want to equip on action bar:
Flare 2 - (Required Level: BLM R25, Action Points Required 10)
Flood 2 - (Required Level: BLM R25, Action Points Required 10)
Aspir - (Required Level: BLM R25, Action Points Required 5)
Bio - (Required Level: BLM R25, Action Points Required 5)

Under this scenario they can allow class identity and at the same time address class balance by using action points to limit how many powerful abilities a player can equip.
Now, of course, the conclusion will be drawn that you have fulfilled the logical requirements to even consider equipping these actions:
Requirements:
1. Advance class quest completed
2. Appropriate arm equipped (staff or whatever)
2. Rank 25 Black Mage achieved

The armory system already gives you more action points as you level up so you would just continue to grow and develop your character.