One of the problems with armors in destiny is that they are not unique in any way other than how they look, that can be changed with ornaments. Adding armor set bonuses like gambit armor can make armors unique and make getting armors interesting. These set bonuses can be as simple as adding stats like +10 mobility to more complicated bonuses. And you can add more sets with every new armor introduced with new activities. Just one more reason to be excited about new loot. And this can replace the limited seasonal mod system.