The same is true for the interoperability converse: gLite clients have signed VOMS-style ACs (inside their PCs) that cannot be traded for signed SAML assertions without the involvement of a hypothetical third-party attribute authority, the implementation and integration of which is also non-trivial.
Thus, for all of our proposed work on profiling service-endpoint-mechanisms, we will have achieved very little in regards to real-world interoperability.
-Duane