We already have XML-RPC working inside AOLserver. XML-RPC, SOAP and any other "web services" stuff really runs in the server layer. The XML-RPC or SOAP service just provides hooks. The applications decide how to use these services.
After OpenACS 4 is released there will be efforts to extend the functionaly with these type of features. There is also nsjava that allows Java to be used in AOLserver so that could also be used. The important thing is that when someone really needs this feature it will be built. Right now it is more of a "let's see what we can do" kind of project. The "web services" area is just getting started.
I am sure after OpenACS 4 rolls out, developers will find ways to enable communication and collaboration between OpenACS 4 and any other web services/toolkits such as ACS 4.6, Zope, etc.
