It's very experimental--I can make it dump core--but it's the start of something moderately nifty. Combine this with boxcarring, and you're beginning to get some decent scalabity and throughput.
Binary Data: I also spoke with several of Flight Gear developers (all very cool folks), and discussed the possibility of XML-RPC without any XML. Basically, a client and server could negotiate away the XML layer, and transmit raw binary data structures to each other. You'd keep all the fun features of XML-RPC (the introspection, the dynamic data, the 750-line clients), but get enterprise-grade RPC when you really needed it.
The hard part of this would be the design, not the implementation. How do you hide the funky new features from the less-advanced clients, and how do you activate the new protocol?
Introspection: I wrote a script called xml-rpc-api2txt. Give it the URL of a server, and it will print out a nicely-formatted interface specification, complete with documentation. I fixed it to play nicely with Meerkat, too--O'Reilly was preformatting some of their documentation strings, which was messing up Perl's formatting commands.
Now, who wants to hack this script to automatically generate C++ and Java classes for a given server? :-)
Community: Yikes! Things are really starting to move. I got piles of e-mail today, half of which contained patches and the other half of which contained great ideas.
SourceForge: Is full of bugs.