[c-smile]

> lack of browser engine implemented basic UI elements as default HTML.

I'd argue that browsers already have full set basic UI elements.

But the thing is that "basic set" is different for each developer / site and that is OK.

Attempt to make a browser to include everything is a path nowhere. Today we have carousel as the thing, tomorrow something else.

That's the moving target. And don't forget about versioning. Each feature has to have a fallback:

   <carousel>
      ...
   </carousel>  
   <nocarousel>
      ...
   </nocarousel>

Old browsers and old machines are still there.

Instead we should have really handy component system like

   <section class="carousel">
      ...
   </section>  

   <style>
      section.carousel {
        controller: Carousel url(/js/carousel-desktop.js); 
      }
      @media handheld { 
        section.carousel {
          controller: Carousel url(/js/carousel-mobile.js); 
        }
      }  

    </style>