Sorry for taking so long to respond. As I’ve said, been a busy week. I’m assuming that’s what it’s supposed to look like?
How would the outer shell work then? Would you have to use custom data and have two instances of the mesh, one for the inner shell and one for the outer shell? You said you could use stencils for the rim erosion too.
Also, I made an outline using PP, although it doesn’t match the outline created in the article, which makes sense. It’s detecting edges, not gonna be able to detect pixels if they’re invisible.
Does that mean that it would have to use custom stencils, apply that stencil onto the inner shell (which could possibly be an instance) and then scale the PP outline from there somehow? Like wouldn’t you still need to grab the normal to get the direction the edge is facing? 
I know you said the rim erosion wouldn’t be dependent on edge detection, but from what I’ve researched, you can get edge wears using Sobel or whatever edge detection algorithm, can’t remember where I found it but saw something similar about edge detection in general here, and I already have an outline PP material. Theoretically couldn’t I just grab the outline I made, and instead of having a color there, somehow apply the rim erosion gradiant to it, play around with the alpha and scale of it to give that effect?
Otherwise I’m not sure how you’d make the outer shell the way you described it? Unless, am I supposed to have two instances then? 1 for the inner shell, 1 for the outer shell.
Thank you.