I'd like to see a system like Qubes but defined declaratively rather than in a GUI. The Qubes templates are sorta declarative through a system called Salt but the OS as a whole (as far as I can tell) is not. I tried getting a NixOS VM running in a NixOS host, all declaratively described and pushed to a machine, but I never could get it working with that extra layer. I'll have to try it with Consfigurator.