Another thing I've always thought would be cool would be "Roll Synergy".
Roll an 11 on both BLM and THF rolls and gain "Magic Critical Hit Rate +10%"
Roll an 11 on both SMN and BLU rolls and gain "Occasionally Absorb Magic Damage"
Roll an 11 on both Courser's and RNG rolls and gain "Recycle +15"
Roll an 11 on both DRK and PLD rolls and gain "Counter +10"
Roll an 11 on both SAM and Tactician's rolls and gain "Zanshin +5"
Ya know, stuff like that. And I guess maybe not give EVERY set of 2 rolls a special bonus because that would be over 600 buffs to think up. But yeah, like maybe just the ones that make sense.
Aaaaand, once they give COR 3 rolls at a time, there could be a whole mind-boggling vortex of potential double synergies.
11 rolls on BLM THF and DRK gains "Magic Critical Hit Rate +10%" and "Magic Critical Hit Damage +10%"
11 rolls on WAR PLD and THF gains "Counter +10" and "Quadruple Attack +4%"
Have I thought of a bonus for every combo? Only about forty five of them. Charts available if a Dev thinks this is a cool idea.