Note that this is much of the idea behind Rust (which is used by this series): browsers are too large and difficult for humans to guard against the presence of vulnerabilities, so we use software (i.e. compilers) to do it. Compilers have a much longer attention span than humans do.

Sandboxing can also achieve this, although at a much more coarse-grained level.

That said, i don't have any strategy at hand regarding browser complexity, but i believe as it gets more prominent, the change will come. At least i hope that the browser i'll be running in 5 years would be a saner piece of software.

What I'd like to see is support for more general, compiler supporting infrastructure. A platform where you could develop your domain specific languages and data structures that are then transformed to native environment. Kind of like JavaScript is used as a transpiler target, but you still need to have loads of functionality on top of browser base.

Then there could be ways to tag your data with semantics (this text is a heading, this is a link), accessibility, editorial intents (text select, copy/paste) that browser could use to display for specific devices and provide interaction (typing, touch).

Since browser is a place to present and produce almost everything digital, not one standard body nor a standard can provide this. HTML/JS/CSS was borne into what it is today for few, narrowly scoped purposes and is creakingly, laboriously converted into different thing each time you open a web app.