Today we can only build "all of" engine package. this feature is about allowing to build a subset of the rpms, thus providing errata with a "package", but with a partial set of rpms. goal is to be able to z-stream only a subset of the rpms when critical fixes are needed in a focused way.
after talking to moran it is an internal thing of the build system they will verify the bug
the 3rd party dependencies are in a different package now. we're working on moving the ui to be based on the REST API, which will enable making it a separate package as well.
i think we are as good as we'll get now till we split the gui. closing.