Ain't gonna happen. Or, if you prefer: Already happened.
Right there in his own essay is the reason.
And that’s exactly where we are with Ajax development today. Sure, yeah, the usability is much better than the first generation DOS apps, because we’ve learned some things since then. But Ajax apps can be inconsistent, and have a lot of trouble working together — you can’t really cut and paste objects from one Ajax app to another, for example, so I’m not sure how you get a picture from Gmail to Flickr. Come on guys, Cut and Paste was invented 25 years ago.
See, Ajax gives you the capability to turn a perfectly good hypertext application into a miserable facsimile of a 1980's PC. And you're not going to fix Ajax by adding a bunch of new APIs. Applications need more constraints, not fewer.
Think how absurd it is that you can't copy a picture from GMail to Flickr. The tools are right there, but the application designers do not leverage them. a) Right click photo in GMail. b) "Copy link location". c) Paste hyperlink into Flickr. d) Flickr either downloads photo from GMail or references it. No new APIs needed -- it's all just hyperlinks.
It's great, and necessary, to extend HTML with rich widgets. We'll never capture them all, declaratively, in a common HTML. I am, even as we speak, constructing a Flash widget. But the web is the platform. Any time I push information deep into my widget -- text that could be searchable, graphics that could be linkable -- and hide it from the web, I've failed to leverage the platform.