I have a small tool called compare_pkglist.py[1] which comparing packages between two build service project and it able to show the diff of package, this tool helps me to understand how many package I've missed and missing updates, it needs an improvement of the output format; show new package only; always check linkinfo; etc.

[1] https://github.com/openSUSE/osc-plugin-factory/blob/master/compare_pkglist.py