heading in a completely different direction that what you were aiming for, but the declarative distros (currently a subset of immutable distros) like NixOS and Guix are trying to solve just this sort of issue – their main focus is on dealing with development environments but a lot of people have been enjoying them on desktop environments as well
ex. with NixOS, your entire system configuration is stored in one master config file /etc/nixos/configuration.nix (that you can optionally keep synced with git) – the main config can be modularized (ie. break out the hardware definitions into its own include so you can still use the master config on both desktop and laptop) – and Nix has been making big strides with Home Manager, their own way of being able to collect and define all of your home directory config files and theming
currently, NixOS is not for the faint-of-heart, documentation (both quality and lack of) regularly gets critiqued – NixOS and Nix package manager are all configured in the Nix language, a functional language used nowhere else
Guix comes out of the GNU project so dealing with proprietary drivers is harder than it needs to be – Guix is configured in Guile Scheme