What I would really love is to see XAML-like layout in the browser.
CSS is a mess I can never wrap my mind around even with the flex model. Whereas the XAML model is much simpler (a measure pass to size components, an arrange pass to lay them).
I think css is mostly a sane low level layout system (which allow you to produce whatever pixel you want, like opengl or whatever) instead of a predefined component system. It will never have those nicely designed components buildin (because it is not its goal). And the complexity price comes from the flexibility it demands.
