I'm concerned that your punting the integration work with the xmlrpc extension. Especially since there is work happening on xmlrpci which provides and OO api to xmlrpc. Can you at least do a review of the extension apis to see how integrating them will affect your design, and also note the differences in your api from xmlrpci.
I'm also concerned about forcing docblock documentation to export a class. I think there should be an api to set what your going to export that can be optionally used instead of adding the docblock params.
Also for something like xmlrpc It would be good to see at least some sort of compatiability testing goals with implementations in other languages since thats generally the purpose of using xml based rpc.
Your also not following the page docblock standards and some other areas where your not following the coding standards, but thats not a big concern.
This is a conditional vote to summarize:
Add an api for setting up a server without introspection
Add extension support or at least review how doing that will affect your design, especially from a speed aspect.
I would also really like to see a compat test against the spec testsuite if there is one and if not at least a basic test against another language's xmlrpc implementation.