FYI, just in case you guys weren’t aware, RetroArch can also load the MAME artwork/layout format now. It’s significantly more complex to make one than a typical RetroArch overlay, but it does give you some more flexibility (you can specify multiple “layouts” for things like with and without glass glare/reflection) and you can hardcode the screen opening size/location instead of users needing to set it themselves.
However, they currently only work with the GL driver, and complex multipass shaders get screwy scaling with them.