GSS-Proxy works well in F19 for both rpc.gssd and rpd.nfsd using gssproxy-0.2.3-5.fc19.x86_64, but it requires the following changes to the gssproxy.conf file to make it operational:
https://git.fedorahosted.org/cgit/gss-proxy.git/commit/?id=7201cabaf0c59b2f5...
An updated release would be good for newcomers ;)
-A