I drafted a proposal for when it is ok to use Conflicts: (almost never):
http://fedoraproject.org/wiki/PackagingDrafts/Conflicts
Keep in mind that while it is not stated in the Draft, the kernel is
considered a special case, and I feel strongly that most (if not all) of
its existing Conflicts: will be approved.
Fedora Packaging Committee Members should vote via email on this issue,
as we did not have quorum in the IRC meeting to vote.
~spot