It looks like Docker support is still a paid feature? That's disappointing. I had written a blog post outlining how important docker support was and explaining how little work it was to get working, and at the time the maintainers agreed it should be a free feature, but it seems they've changed their minds.
We've not changed our minds on docker becoming a free feature eventually. We just didn't update the pricing yet, but this is planned for the near future.
IHP is really easy to package with nix nowadays. In fact the official docker building also just uses `pkgs.dockerTools.buildImage` and calls nix-build :) Most people with nix experience can easily figure out how to do exactly the same thing as the "official" way.