I just want to give heads up that today, my PR [1] allowing to set SOURCE_DATE_EPOCH environment variable during build of RPM was merged into redhat-rpm-config. This means that some packages might have a bit more reproducible builds.
This was triggered by this ticket [2] and subsequent discussion
on Ruby-SIG ML [3]. Please keep in mind that while your packages
might benefit from this if it respects the environment variable,
this is *not* part of any broader reproducible builds effort.
Vít
[1] https://src.fedoraproject.org/rpms/redhat-rpm-config/pull-request/57