I think XAML is that format, but it isn't without its pain points. You pretty much can't do animation without a tool like Blend unless you're a sadist.

It looks like Xamarin uses .AXML for Android (maybe a XAML flavor) but has to adhere to Interface Builder for iOS (http://docs.xamarin.com/guides/cross-platform/application_fu..., specifically the Visual Designer section). XAML likely won't gain any traction on those platforms though due to NiH on all sides. HTML/CSS is likely as close as we get for now but that isn't a "native view" in any of the platforms mentioned.