The End of XHTML

Long Live HTML. Only 6 or 7 years ago it looked as if HTML was to be supplanted by XHTML, and now HTML survives and, in the taxonomy of HTML, XHTML turns out to be just another truncated branch.

While we recognize the value of the XHTML 2 Working Group's contributions over the years, after discussion with the participants, W3C management has decided to allow the Working Group's charter to expire at the end of 2009 and not to renew it.
Frequently Asked Questions (FAQ) about the future of XHTML

A central aspect of HTML5, and the retreat from XHTML is the abandonment of decentralized extensibility:

HTML 5 has a number of extensibility mechanisms, but none yet that satisfies the requirement XML namespaces was designed to address of decentralized extensibility - allowing parties to include their own elements or attributes in content without risk of name collisions (whether those names are the result of a consensus process or not).
Frequently Asked Questions (FAQ) about the future of XHTML

Is this a good thing? Maybe. XML survives and organizations retain the ability to give access to priority data without giving access to their database.