Would there be interest in a cross-platform GUI written in C++ or Rust that uses HTML/CSS/JS as its layout and animation language, but runs natively on CPU/GPU without a browser layer?
If you're going to do that, maybe consider versions of those intended to work as a native GUI layer, but which are as easy to develop as the web.
They’ve been evolving for so many years that the initial intent behind their design isn’t very relevant. Especially if you consider modern tooling, language versions, webgl, svg, canvas, and so much more.
If there is one tech that we need to bring back from the dead, it is XUL
(XUL is the GUI toolkit powering Firefox, or at least was until they ripped almost all of it out and replaced it with "modern" (gag) HTML+CSS UI)