And now for something completely different I've implemented PEP517 support for the SCons-powered build system "enscons", quite possibly the most different pip build backend available. It should be able to build itself and rsalette (another enscons-using package) using pep517. Note the newly required env.Default() that enscons needs to return the target filename to pip. Due to SCons limitations enscons may not be able to build .tar.gz sdists on Windows. enscons is an experimental Python build system that runs on top of SCons, a Makefile replacement. It is able to build C. It should be much easier to customize than a setuptools-based system. I originally wrote it so that I could experiment with the wheel format without having to hack on setuptools. It might be useful to you if you have a package that has a complex dependency tree of generated code between the source and whatever ends up in the wheel, if you want to build more than one wheel from a single source tree, or if you have other needs that just don't fit into setuptools. enscons also has a setup.py emulation that supports "setup.py develop". The pep517 package is pretty cool. Thanks! I would call these pep517 powered builds "pluggable". Daniel Holth