Sun NeWS should have been that GUI standard, thirty years ago:
https://en.wikipedia.org/wiki/NeWS
There was a simplicity and purity in its approach to front-end interactivity and rendering that completely eludes the HTML+CSS+JS stack we're now stuck with. As the Wikipedia article states...
"NeWS was architecturally similar to what is now called AJAX, except that NeWS coherently:
used PostScript code instead of JavaScript for programming;
used PostScript graphics instead of DHTML and CSS for rendering;
used PostScript data instead of XML and JSON for data representation."
PostScript is basically a graphics-oriented Forth, so it's kind of a weird language to write directly... But it would have been great as a target for all sorts of interesting compilers and GUI tools.