The difference though is if the intent is for the markup to be styled, it will be written differently. For example, take a look at the WPF built-in controls.

The difference though is if the intent is for the markup to be styled, it will be written differently. For example, take a look at the WPF built-in controls. Those are written in very clean XAML. Easy to read, style, and modify. I'm sure they could have made it difficult, but their intent was that you'd modify the built-in controls. If they want to do this with the UI, they could do it. The theming you could do with this could be incredible. I doubt this is something they're going to do for V1 (if ever), but I can dream.