Several of the new WS-* specs introduce WSDL extensions that somehow need to be represented in the UMD model. After a short discussion with Thomas, we decided that any forthcoming project would benefit from a clear separation between the the base UMD and it's extensions. (Think of tools for instance).
In it's most simple form we came up with namespace aware extension that can be mapped to any UMD model element:
I.e. a WSA meta data extension on operation level: