Funny, his list of things that IE9 supports reads like a list of cool HTML5 stuff you'd want to use. The "things it doesn't support" list looks like something he made up on the spot (though clearly they're all real things that somebody has proposed putting into web browsers.)
But it's all stuff that doesn't belong in web browsers. (OK, maybe WebSockets). If it were up to me, now would be the time to actually standardize some of those things on the first list so that they work cross browser. Then we're done.
* The improvement to forms and forms management are long overdue and extremely interesting, especially for mobile phones.
* The History API is extremely needed right now, as it allows sites to have their cake and eat it too in regards to JS-drive Single Page Interfaces still mapping to actual resources (bookmarkable, and sharable, and not blowing up if there is a JS issue or JS is disabled).
* The File API is an other domain which is full of pain right now for web applications: the only way to correctly manage files without ending up wanting to shoot yourself is to use Flash, that's how bad it is.
* Audio Data, WebGL, WebWorkers, WebSockets and AppCache are necessary gateways to move more "desktop-class" applications to the web (fully online, or offlined from the web).
The stuff IE9 is missing is actually more helpful and interesting for the vast majority of content-oriented websites (not to mention web applications, WebGL has infinitely more potential than Canvas, let alone SVG) that the stuff it does have.
History API is huge: ability to use real permalinks and back/forward in a dynamic web app without full page reloads. (We all want to get rid of the those damn #!hashbangs.)
WebGL opens up far more possibilities for cross-platform gaming than <canvas> and SVG combined.
Some of the others, admittedly, are only useful in edge cases, or are just plain pipe dreams (<device> in particular). But many are already supported by non-IE browsers, and all the other players have clearly broadcasted their intent to keep improving and evolving. Microsoft (AFAIK) has yet to do any such thing.
(Grandparent: Just because something isn’t in (all) browsers now doesn’t mean it “doesn’t belong” or, less straw-man-ish, that it wouldn’t be useful for some browsers to support; not all browsers need to implement everything, that’s why we have feature detection. But having IE, still the #1 most popular browser, on board really opens doors.)
I wasn't aware that progress was being made; nothing would please me more than device APIs in JavaScript. I don't know of any working implementations in the field, though.
But it's all stuff that doesn't belong in web browsers. (OK, maybe WebSockets). If it were up to me, now would be the time to actually standardize some of those things on the first list so that they work cross browser. Then we're done.