Is there any use for this freedom check unless the packager has nonfree packages available on their system? If blacklist has foo:foo-libre:, listing foo-libre in dependencies will make updates from foo-libre to fixed foo harder, if blacklist has foo:: then the packager cannot install the package or its dependencies without using non-Parabola repos with the nonfree package. Or is there a different case when this check is useful?

(It also doesn't seem arch-specific unlike the rest of what libremakepkg does.)

The checks will include things more than they currently do. For example, checking license files, for some common machine-checkable issues in the source directory, etc. Also, it dissables networking during build() and package(), as some software cleverly tries to download binaries during the build process.

Done in git; invocation is almost identical.