BindableBehavior.cs

public abstract class BindableBehavior<T> : Behavior<T> where T : BindableObject
{
    protected override void OnAttachedTo(T bindable)
    {
        if (bindable != null)
        {
            this.InheritsBindingContextFrom(bindable);
        }
        base.OnAttachedTo(bindable);
    }
}

BindableObjectMixins.cs

public static class BindableObjectMixins
{
    public static void InheritsBindingContextFrom(this BindableObject target, BindableObject source)
    {
        if (target == null) throw new ArgumentNullException(nameof(target));
        if (source == null) throw new ArgumentNullException(nameof(source));

        source.BindingContextChanged += OnBindingContextChanged;

        BindableObject.SetInheritedBindingContext(target, source.BindingContext);

        void OnBindingContextChanged(object sender, EventArgs e)
        {
            BindableObject.SetInheritedBindingContext(target, source.BindingContext);
        }
    }
}