I just spotted this interesting article comparing the emerging HTML V5 and XHTML V2 standards. I think the debate about the strengths and weaknesses of each approach is an interesting one. HTML 5 seems to be about making web development as easy as possible, with the metrics for ‘easiness’ being based on the problems of current web application development practice. XHTML 2 emphasises modularity and the refining of the MVC paradigm as applied to web development.
Each approach has its pros and cons, but my initial feeling is that HTML 5 focuses too much on rapid development, and not enough on the long term issues like providing a basis for creating sustainable and maintainable software.