This looks great, but it looks like it'll be a bit of a hassle to generate the layer yourself. If KiCAD gets a "generate heating layer pattern" feature, this would become trivial.
Then again, I don't know how much I want to bother with masks and placing things myself, given how cheap JLCPCB's assembly service is.
I wonder if it'd get hot enough to print this on a separate board and just lay the working board on top.
My buddy and I were talking about this. At this point kts basically just the hot plate technique, and you'd just be making your own hot plate