I can't speak to the implementation of this, but I am in favour of the
approach in general, with one caveat: I think it is important to
implement this in a way that makes it possible for users to keep
*individual* retired packages around. Blacklisting
fedora-retired-packages is too broad a brush from the user perspective,
and will make it much harder to identify problems.
A question regarding this: What would happen if an update to
fedora-retired-packages obsoletes a package that is present on my system
but listed in dnf's excludepkgs?
Christopher