The user opens a URL that downloads an 'app' and all it's dependencies. So, to start with, you'd have dozens of UI frameworks, network libraries, parsers, etc on your system. Some of them would be great, others would be terrible. Slowly, as the best ones bubble up to the top and become 'standards', each of dependencies would disappear. Developers would settle on one of a few different engines and frameworks. Apps would be the content, a few scripts to drive the engine, and a manifest to tell the user's computer which standard engine to download.
Which would essentially be the modern web as it is now.
As soon as the author started explaining problems about browsers I started thinking about solutions. And I realised that "we" already tried to solve this problem with plugins. Flash, Java applets, Silverlight, etc. were all envisioned as solutions to these problems. And it doesn't take too much brain to realise they all failed (at least in the popularity contest).
Restful nature of the Web is giving good structure on which to build and time shows that evolution, instead of forcing one good solution, is much better way for technology adoption when it comes to the masses.
What you describe would be some kind of a natural selection among lower level abstractions. Maybe they would indeed converge into a "few standard engines", maybe not. Either way, they wouldn't force your hands: you could always use whatever UI framework or network library you want and still distribute your app as a simple URI.
In contrast, "the modern web as it is now" gives you a single built-in layout engine and not even a chance to implement network libraries. And that's exactly my point: For a document viewer, that's fine. For an application distribution platform, not so much.
Sometimes I dream of an alternate future where SUN weren't asshats and Java won and we're all running applications that come with maven POMs. Then I remember how badly the average web developer can bungle simple static HTML and realise how happy I am I don't have to debug spaghetti XML.
Which would essentially be the modern web as it is now.