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This isn't the cleanest approach but at least it works.

One can define two different templates (each of them contains `ItemsControl` with single difference in `ItemsPanelTemplate`) and switch between them as needed with a simple "selector":

C#:

```csharp
public class ViewTypeTemplateSelector : IDataTemplate
{
    [Content]
    public Dictionary<ViewType, IDataTemplate> Templates { get; }
        = new Dictionary<ViewType, IDataTemplate>();
    public IControl Build(object data) => Templates[(ViewType)data].Build(data);
    public bool Match(object data) => data is ViewType;
}
```
xaml:

```xaml
    <ContentControl Grid.Row="0" Content="{Binding ViewType}">
      <ContentControl.Resources>
          <DataTemplate x:Key="itemTemplate">
            <TextBlock Text="{Binding}" Margin="2" Padding="2"/>
          </DataTemplate>
        </ContentControl.Resources>
      <ContentControl.DataTemplates>
        <views:ViewTypeTemplateSelector>
          <DataTemplate x:Key="H">
            <ItemsControl ItemTemplate="{StaticResource ResourceKey=itemTemplate}" Items="{Binding Values}" DataContext="{Binding $parent[Window].DataContext}">
              <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                  <StackPanel Orientation="Horizontal"/>
                </ItemsPanelTemplate>
              </ItemsControl.ItemsPanel>
            </ItemsControl>
          </DataTemplate>
          <DataTemplate x:Key="V">
            <ItemsControl ItemTemplate="{StaticResource ResourceKey=itemTemplate}" Items="{Binding Values}" DataContext="{Binding $parent[Window].DataContext}">
              <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                  <StackPanel Orientation="Vertical"/>
                </ItemsPanelTemplate>
              </ItemsControl.ItemsPanel>
            </ItemsControl>
          </DataTemplate>
        </views:ViewTypeTemplateSelector>
      </ContentControl.DataTemplates>
    </ContentControl>
```