Proposal: Simply specify a XHTML lax, or XHTML+RDF Namespace and Schema

To put a point on Mimasa's work with a potentially rash proposal: why not 
just specify a XHTML+RDF or XHTML-lax namespace and schema and ask people 
to use that? Problem solved!?

Mimasa has already provided the XHTML-lax schema, I even have it running as 
an (temporary) experimental validator at:
  http://policy.w3.org/xsd-xhtml1-validate

What objection would the HTML or RDF communities likely raise? If none, is 
it just a matter of assigning the action to do it, and to find the 
resources to maintain a validator service?