Substitution Groups Reconsidered

We are having trouble finding a Java data binding framework, either open
source or commercial which supports substitution groups. Castor seems to be
a leader in this area and it currently does not support them. Does anyone
have any suggestions? Is this reason to reconsider substitution groups in
SAML 1.0? We have seen some commentaries suggesting that substitution groups
are an XML schema feature to be avoided. See for example:

http://www.geocities.com/kohsukekawaguchi/XMLSchemaDOsAndDONTs.html

Hal