Somehow there needs to be an API so other modules can call and accept XML-RPC calls. There should be a way for a module to register and services it can deliver via XML-RPC so the XML-RPC handler knows what to call when it receives a request.
It should also be possible to abstract this so that the same API can be used for SOAP procedure calls if that feature were to be added.
I am willing to help test and work on this if you need. Eventually I want to work on XML-RPC interface for the CMS.
Also, we should work out a standard set of helper procs for ns-xml so they can be used consistently throughout ACS.