Since ::gentoo is the only repository governed by the PMS, can't we make repoman do this? The problem with requiring "repoman --force" for an in-place dependency change is that repoman generally won't have access to the unedited ebuild; but for ::gentoo, we can probably hack something together in git. Have it source the old and new ebuilds, and compare their dependency lists.
It won't work outside of a git repo, but it will work in the one place that really matters.
