The build process is essentially working though the resulting installed package does not work quite right. The biggest problem is lack of keyboard/mouse input. There are also issues with some plugins scarfed from Raspbmc. But at least the build is stable enough to allow XBMC to start up and even start pulling in automated updates.
Since the build is stable I can now start meaningful discussions on XBMC forums about how to fix some of the remaining issues. I think the keyboard/mouse issue may be an issue with how vchiq is either used or not used. But that's a guess as this point.
Still, it is nice to see the XBMC start up graphic show up and the menus displayed and the automated updates start running. That's a big step forward.