I suppose you are referring to this WPF functionality https://docs.microsoft.com/en-us/dotnet/framework/wpf/contro..., and similarly in UWP: https://docs.microsoft.com/en-us/windows/uwp/design/controls...? While it looks powerful, I have to say that the Xcode interface builder and code annotation approach has a lot less friction.

Yes, exactly that, but you don't need to go the full way.

It depends on what kind of rendering one wants to present to the user/developer, even with DesignerAttribute one can provide a custom rendering for the control.

Here with a forms example, but similar way can be done for the XAML variants.

https://msdn.microsoft.com/en-us/library/ms171824.aspx