A friend of mine built something like this 10y ago or so - a fuse filesystem backend for a NixOS/Nix-store with built-in caching. So whenever you started an app

A friend of mine built something like this 10y ago or so - a fuse filesystem backend for a NixOS/Nix-store with built-in caching. So whenever you started an application/version you never ran before, it was just downloaded on demand and the only thing you might have noticed is a slight delay in startup duration. By just regularly updating the configured Nix-channel it was always the latest software of this channel running in the local environment.