How is it that much different than using OS APIs to do common tasks like text, windows, buttons, scroll bars, etc? If you really want to do pixel level stuff, there is canvases and images and SVGs.
How would I replace html in the browser? Create a new rendering api in canvas? Can it be done? Sure. Will it be pretty? Not so sure.
Imagine your operating system can only compile one single language: Perl. And with perl the only way you can render anything on the screen is with a QT api and QT UI primitives.
Programmers can still do anything within this ecosystem. Technically you can have perl as compile targets for any other language. Lets also pretend that QT has this little UI element called canvas that has a api allowing you pixel level control.
While technically you could do anything in a platform like the one I described above, I'm sure you can easily see why it's still bad.
