I think this is something the writer of the article would be delighted to find: https://github.com/railwayapp/nixpacks
If it's using nix for building - there's multiple ways to DIY turn that into a docker container, like pkgs.dockerTools.buildImage or nixpacks:
I think this is true for Nix in the deployment/ops space, where debugging a broken build can be very frustrating. Language improvements are going to be less useful for app developers, the Flake learning curve is not going to get better with a type system.
Perhaps something like heroku buildpaks (https://github.com/railwayapp/nixpacks ?) would help devs get on the Nix train.
I like Fly.io but I wish it offered something with Nix in the build process like Railway has recently introduced.