We need something like this for home, I hate that programs like steam and firefox place themselves directly into home instead of ~/.config and ~/.llocal.
I even move my personal themes to /usr/share/themes because not everything works with ~/.local/share/themes and needs a ~/themes directory instead.
Thanks, I just went down this rabbit hole and discovered xdg ninja and managed to clean most of my home, I even found a useful script that launches steam on a fake home directory on .local.