While this package was removed from unstable in favor of unanimity (which didn't get processed in time to be considered as part of the release of Stretch), I figured out the solution to this RC bug, as unanimity was showing similar issues.
I didn't realize that pybuild itself does build-system detection and its detection is not reproducible when there is more than one possibility. In this case, when it detects "distutils", the build works. When it detects "cmake", the package comes out empty. The solution (and what was done for unanimity) was to explicitly set it to "distutils". Just posting here for the record in case someone else stumbles across a similar issue. -- Afif Elghraoui | عفيف الغراوي http://afif.ghraoui.name