The thing is, Destiny's "classes" aren't even really that. They don't really differ too much and heck, you can change their Armor, Recovery and Agility to your leisure, within the classes limits. There isn't a whole lot that screams these classes to be different. I have little trouble switch from Warlock to Hunter to Titan. It's not quite a true RPG, but it works. I mean, people wouldn't be playing if it didn't. So to put in the healer subclass for a warlock wouldn't really be too beneficial. Don't get me wrong, I think this is a great idea. I typically play a healer in class type games, but in a game like destiny, it's just too out of place. All but one of the subclasses so far are offensive, Defender being the exception. Voidwalker is heavy area control, Gunslinger is heavy precision, Striker is also heavy area control, Sunsinger is support for yourself (and teammates if you're a good player) and blade dancer is close range combat. None of these classes really differ to different places. As much as I'd like this, it just wouldn't fit.