Sean Corfield mentioned this entry from his blog on the Fusebox 5 dev mailing list. I had read over the entry the other day when he posted it, but I'm still only grasping the relevance of it.
Putting the extensible in XML, it almost looks like Sean is calling Model-Glue THROUGH Fusebox5. Now, how exactly does that work? Ahh, it's the beauty of those lexicons - they're more than meets the eye, apparently.