While I appreciate Mark Pilgrim's This week in HTML5 land weekly reports, there's one underlying thread that occurs every month that Mark doesn't necessarily touch on: the issue of distributed extensibility. You know, the namespace, XHTML, SVG and MathML et al thing that doesn't go away.
For instance, catching up on my HTML5 Working Group public archives reading, I found this gem from Chris Wilson of Microsoft:
You are correct, we cannot definitively say why XHTML has not been successful on the Web. However, I do believe that part of that lack of success is due to the less-forgiving XML syntax, and part of it is due to the degradation story (or lack thereof) in browsers and versions that don't support it. (I don't want to turn this into a pro/con XML debate either.) Part of its success in the future will be due to the important and focus it is lent by all of the major browsers. Perhaps I am misreading the tea leaves; I don't see much interest in XHTML's future from the other browsers. I do think XHTML would have a lot of positives as a basis; however, it does have a few negatives, and it would need to be a universal push if it were to be successful.
I would say that we can definitively state why XHTML has had limited success on the web: lack of implementation and support in IE, one of the web's major browsers. In addition, none of the other browsers have said that they aren't interested in supporting XHTML in the future. The fact that Microsoft's main IE architect would make this statement leads me to believe he should be in politics.
And I'm only up to August in the archives. What other delights await in September and October...