Hi thwak; That`s pretty much my understanding of it. My general thought is to simplify the persistence mechanism.
Either by eliminating the image file, and/or by simplifying the union setup, or by eliminating it all together.
Mount is kernel space, and I`ve used Union-Fuse but it`s user space. Linus Torvalds said it`s no solution.
As I`ve said... A union is not required if the apps are portable no-install. Seemingly a much better O.S. setup.