Originally Posted by
DoctorMog
Square enix had a card game on facebook which might have useful mechanics that could work here.
Certain sets of four classes in a party give a bonus. Each party could have two of these effects active (4+4)
THM THM BLM BLM - "Dark Delight" Magic attack bonus + 5%
WHM WHM CON CON - "Holy Hand Grenade" Healing magic potency +5%
PLD WAR DRG MNK - "In the heat of battle" Evasion & Magic evasion + 5%
WAR WAR DRG MNK - "Heavy Hitters" Crit attack bonus +10%
DRG DRG MNK MNK - "Pain is the game" Attack power + 5%
Anyway, you get the idea.
Promotes different setups because there is no bonus for 3 or 4 of the same job/class. It also promotes the use of classes and jobs together.
Edit: As Indira said, it gives "two or less" of each class in a party a bonus.