Ok I'm not going weight into this because I think its personally all going to sort its self out with a hybrid mix of xhtml 2.0 and html 5.0. Gareth Rushgrove has written much more about the issue and I agree with him too. The fear and misunderstanding around this whole thing is scary. If people actually read the FAQ's they might also get it.
Does W3C plan for the XML serialization of HTML to support XML namespaces?
Yes. The HTML 5 specification says in section 9.1 “The syntax for
using HTML with XML, whether in XHTML documents or embedded in other
XML documents, is defined in the XML and Namespaces in XML
However, see the question below for the relationship between
XML namespaces and decentralized extensibility.
What are W3C's plans for RDFa?
RDFa is a specification for attributes to express structured data in
any markup language. W3C published RDFa as a Recommendation in October
2008, and deployment continues to grow.
The HTML Working Group has not yet incorporated RDFa into their
drafts of HTML 5. Whether and how to include RDFa into HTML 5 is an
open question on which we expect further discussion from the
community (see also the question on decentralized extensibility).