Glad you're interested. I don't think you missed anything. I only made the mock-up a few days ago. Until then, it was a bit of an abstract idea. Even to myself.
As I was making the mock-up, I immediately realised there's lots of unresolved issues which I avoided/kept vague. So yeah, this would need some serious thought put into it.
This particular idea was kind of recent in the last few months I think. We've always wanted some way to have better layer ordering and bone control "outside" of bone layers but I think this is the BEST visual description for a solution.
