For the fedora-atomic work, the only not-in-Fedora package is shadow-utils because it requires a patch, that still lives in my walters/rpm-ostree COPR.
Patch is linked from my post here:
http://lists.alioth.debian.org/pipermail/pkg-shadow-devel/2014-March/010099.html
Also, some discussion in the glibc bug:
https://sourceware.org/bugzilla/show_bug.cgi?id=16142
What I'd like to open is a discussion about whether /usr/lib/passwd is the right thing long term. I think it'd be very useful to support it short term, but it's not perfect.
The main case where it breaks is when you have a daemon that runs as non-root and saves state, so you give it its own system user, but not a reserved uid. Daemons in this class will have their uids effectively ordered by package installation order =/