Part of Fedora's role in the larger Free Software community is to drive convergence and improvements in upstream projects. This manifests in various ways, such as getting projects onto the same shared library versions, etc. In this instance, if our tooling could be signinficantly improved by using revision control instead of tarballs (and I definitely believe that is the case) we can help move upstream.
For example in GNOME it would not be a large workflow change to make it a hard requirement that tarball releases on ftp.gnome.org
have a predictable correspondingly named SVN (or hopefully later git) tag.