This question sounds so stupid that I didn't want to ask it in public. Many web-related languages that have idiosyncratic syntax also provide an XML surface syntax. Examples are Turtle (RDF/XML), xquery, OWL 2 (OWL/XML). To ensure that HTML5 can participate in XML pipelines in a standard way, wouldn't it be a good idea to have a standard XML surface syntax for HTML5, with semantics preserved over round trips? Perhaps this even could be done using a set of extensions to XHTML.
Jonathan
