You're right. Browsers are constraining innovation to a top-down approach, where browser vendors try to design and implement alternatives to things like TCP, POSIX.
What would be better is if browser vendors exposed a core low-level API to trusted installed web apps (as opposed to web pages) and then let open source build on that.
For example, instead of coding up IndexedDB and leaving no alternative, just provide proper POSIX, and let the database community do its thing.
Because there's more interest in improving the (publicly accessible) web as a platform than improving installed web apps.
Regardless, to expose such a low-level API would eliminate one of the big advantages of the web: given a browser, I can use any web app on any device. Given, for example, given a TV (which are typically closed platforms, but increasingly often include a fully featured browser), you likely wouldn't be able to install anything that a certain web app depended on (and even if you could, what are the odds that it's been tested on a big-endian platform?).
None of what timbl said in that post (nor what anything, from memory, in that thread said) covered shipping native code to the browser: it was merely talking about privileged web apps, which is a very different problem area (and one that should definitely be explored!).
Yes, my comment was concerning the top-down approach taken by browser vendors, and that web apps need to be empowered with low-level APIs such as TCP and POSIX. I don't think I said or TBL said that we need to ship native code to browsers to do this. We don't. We don't need another language. Javascript is fine. We do need better low-level APIs. We do need to get away from relying on browser vendors to spec and implement everything correctly, because with such a massive surface like they're targeting they won't. We do need to push this responsibility out to the edges. We need to drastically reduce the standard API and move the functionality from high level (as in IndexedDB) to low level (as in POSIX). We need a strong powerful stable small core and OSS must do the rest. That's the general idea. The finer details can be nitpicked and that won't invalidate the general idea. Browser vendors are simply doing way too much.
What would be better is if browser vendors exposed a core low-level API to trusted installed web apps (as opposed to web pages) and then let open source build on that.
For example, instead of coding up IndexedDB and leaving no alternative, just provide proper POSIX, and let the database community do its thing.