There is the alien program to convert binary packages between various formats, but it would be even nicer to be able to take a debian or archlinux build spec and convert it into an rpm .spec file.

Apart from the syntax conversion, this will need some mapping for package names, so that BuildRequires and Requires match the target. Alternatively, we could patch all openSUSE packages to have Provides for names of other Linux distributions (e.g. libqt4-devel Provides: libqt4-dev)

this looks like a good start: https://github.com/jordansissel/fpm/