Darkness could reduce crit chance: Blinded
Water could be a snare that DOES stack with other snares: Soaked
Light could be a bonus to allies (probably only able to be applied with heals,) it would just be like a generic unnamed +8% healing taken: Blessed
I'm struggling to come up with answers for the others... But that isn't the problem. The problem is having to add a mess of new weapons and abilities that do these damage types. And sets.