FWIW, I think that element upgrade is sort of fundamental to the usefulness of custom elements. In a world where most scripts are non-blocking (that's hopefully the modern world we should aim for), I'll effectively expect to walk the tree anyway.
And if I walk the tree anyway, what's the point of custom elements in the first place? One of the key features (at least, to me) of custom elements was being able to harness the HTML Parser to instantiate your object tree. If that's not going happen consistently, then I am not sure custom elements are worth the trouble. IOW, if you're walking the tree, just do the work of callbacks as you encounter dash-separated elements. :DG<
