It would be really cool to take the BLM mechanic of fire/ice balance and apply a similiar function to the RDM class. Possibly have RDM constantly struggling between light/dark energies. Since white magic was founded to help combat black magic. Basically by casting black magic spells you move more into a DD mode and by casting white magic (healing) spells you move more into a healer mode. Of course you would need to give them the infamous Doublecast ability! I thought it would be neat to give them an ability to instantly switch between max DD mode and max heal mode but that would be OP. Of course give RDM access to rapiers/shields.

This is my last idea for now(aside from adding in some sort of skill tree or ff10 sphere grid for further character customization; I dislike being exactly like the other jobs in my FC xD!)