More confirmation HTML isn't going to accrue substantive changes for years...
...if not because of slow specification processes, because it's unlikely the currently most-used browser (IE) will implement the interim stages — in the same way it has yet to fully implement XHTML* (a seven-year-old standard) or CSS2 (which dates back to 1998), both of which are web technologies people persevere with in spite of this. Add to that its implementations are often broken... meaning that what we're stuck working with for "real world" use is a fairly stable, unchanging subset of HTML, has been for some time and isn't likely to change soon.
Well-formed HTML 4.01 plus a DOCTYPE (which one depends on whether you can do without iframes) does just fine, and will continue to do so... far into this century, at a guess. How long did it take floppy drives to die? They're still standard on many machines — and that's hardware, something the manufacturer has to pay for, whereas throwing in some legacy code to support HTML 4.01 in the browsers of the future (with the processing power of the future, even on mobile devices) will be trivial. Not to mention unavoidable, since the majority of webpages out there don't meet validation as HTML 4.01 — they're tag soup.
We've been hearing about XHTML and XML as the future of the web for half a decade now. With the resurrection of HTML 5 as a proposal and real-world support for XHTML 1.1 and 2.0** touring in company with the Royal Porcine Aviation Corps, I move to suggest that for most actual uses it failed. What it succeeded in doing quite well was getting people talking about web standards and the benefits/possibilities of document structure, accessibility, consistent rendering, browsers on mobile devices, etc.
The last time I wrote about markup languages was last December. Far more about XHTML can, unsurprisingly, be found in its Wikipedia article. The current version probably fails neutral POV criteria and is a decent read:
Recently, notable bloggers have begun to question why Web authors ever made the leap into authoring in XHTML, and are suggesting that the W3Cís Appendix C HTML Compatibility Guidelines are a hack. In October 2006, HTML inventor and W3C chair Tim Berners-Lee, explaining the motivation for the resumption of HTML (not XHTML) development, posted in his blog: "The attempt to get the world to switch to XML, including quotes around attribute values and slashes in empty tags and namespaces all at once didn't work. The large HTML-generating public did not move, largely because the browsers didn't complain."
(I don't mean to interpolate myself as a "notable blogger"...)
*IE (including IE7) doesn't support XHTML at all: your code gets rendered as HTML, using the text/html media type. Unless you need XML data structures or can't write well-formed markup without the helping hand, there's little to be gained except being able to say you're adhering to a 2000 standard rather than a 1999 one.
**XHTML 2.0 is notably backwards-incompatible with XHTML 1.0 or 1.1, funnily enough.