The main issue I have with this concept is the different level of support of these elements/components by themes.
Third party commercial themes would not come with templates for these components at all. Some themes might support only subset of components (maybe new components were introduced after the theme was released).
The only way I can see this to work is for every component to have some default, theme agnostic, template. And this might be hard to do, because such template would not be able to use any framework css, any framework js,...
Themes could, of course, override these default templates. But even if they did not override them, the components would still work to some extent.
Is this aligned with your vision?