I don't think a system like this can be implemented until destiny 2. Destiny as it is with its armor and exotics is somewhat shallow when you compare it to something like diablo 3/path of exile when it comes to hear sets or bonuses. I think that destiny has the potential to do something just as unique and interesting with it. So it would make giving up your exotic slot a worth while thing. As of right now, exotics are just too good to pass up. Would a defender give up saint 14 helm in pve for increased agility? Probably not. Would a voidwalker give up up obsidian mind for +2 armor and third eye against minions of darkness? I doubt it. Would a golden gun gunslinger give up celestial for increased recovery? I again don't see that. As of right now, destiny doesn't have the infrastructure to make such massive changes. Gear sets can be awesome, like they are in diablo, but the foundation needs to be right. I suspect we will see something like this in destiny 2. Right now, I don't see major changes coming