As far as I know there is only the starter shell, and the Ghost Edition one. I think it would be cool if you could get others, like there would be a really rare one (RNG anyway) that you can get from Crucible that is Orange/Red and White to match crucible gear colors. There could be another one you can (again RNG) get from raids. Another, and the final one, you can get randomly from any mission/strike. As for the shaders, they are cool, but could you make like shaders that are rewards for certain things, like I remember there was (before the release) an unofficial Titan that looked dressed as a Vex, so I think per say you kill X amount of Vex you get the Shader. In short, make special shaders that can change the design as well as color. All in all I'd rather see the Shells idea in the game rather that the special shaders. I just thought special shaders was an idea, but not a good one cause most people probably wouldn't want their armor design to change.