I think it would be great to have a Pulumi-based Nix deployment stack.
I think Nix/Nixpkgs/NixOS are great, and by far the best way to package applications. But NixOps, I think, is a mistake - it's an over-extension, the technologies behind Nix are perfect and way better than anything else for package management, but merely OK for host management. I actually think Pulumi has some better ideas for this, so it would be cool to use Pulumi to orchestrate deployment of Nix/NixOS stuff.