> Worse, there're no good open source implementations of GPU-based ones. Microsoft ships an implementation as a part of OS (Direct2D) but it's not open source. Linux simply doesn't have an equivalent.

What about OpenGL? I believe that the Firefox/Servo WebRender (written in Rust) also uses OpenGL. But I do believe that the GPU acceleration implementation is more complete on Windows and Mac OS.

> you'll definitely find good free libraries to deal with HTML and CSS, you'll probably find libraries to interpret or JIT-compile JavaScript, but still, the remaining pieces are huge.

I really want to not use libraries as much as possible and do everything on my own. It won't be good as the libraries but I see a lot of value in doing everything myself and learn it.