New functionality has been added to the XAML Runtime in Windows Embedded Compact 2013. There doesn't appear to be an official changelog so below are some of the known changes as they are implemented in XAML In The Hand:-
FrameworkElement.GetBindingExpression - Allows you to get a BindingExpression for a data-bound property. In the XAML Runtime this supports just the UpdateSource method which triggers a manual update of a bound property to it's data source.
System.Windows.Data.Binding is no longer a struct and is now a DependencyObject. It includes extra properties and will eventually expose functionality for value converters.
Control.GetTemplateChild - Used to get a named child control which is part of a control's template.
System.Windows.Interactivity (and related Expression Blend APIs) - Not currently supported in XAML In The Hand.