The UI for exposing input elements of container builds is much easier and cleaner than using plugin steps as you can't present out a multi input option like build arguments. We need to use Buildah as we need a non privileged build capability. We'd like buildah to be a supported option in the build steps. Also you should be able to select the "engine" from a drop down to be able to use say Kaniko in one step and Buildah in another.