This is a concept I like a lot. I would love to register a
listener for a given namespace that would have
associated with it a deserializer and a callback routine.
For example, I could register a WS-Security listener that
could be called by SOAP::Lite when a WS-Security
header is encountered - this could provide an automatic
way of performing authentication. The callback could
conceivably hijack the whole request-response by
returning a SOAP Fault if an error occurred.
This would also make SOAP::Lite quite extensible, and
would be a core differentiator to other toolkits IMHO.