The steps to get this Store UI working are:

1. Add a reference to your Core PCL project
2. Change App.Xaml.cs so that it creates a 'new Setup(RootFrame)' during its OnLaunched:

        protected override void OnLaunched(LaunchActivatedEventArgs args)
        {
            var rootFrame = Window.Current.Content as Frame;

            // Do not repeat app initialization when the Window already has content,
            // just ensure that the window is active
            if (rootFrame == null)
            {
                // Create a Frame to act as the navigation context and navigate to the first page
                rootFrame = new Frame();

                if (args.PreviousExecutionState == ApplicationExecutionState.Terminated)
                {
                    //TODO: Load state from previously suspended application
                }

                // Place the frame in the current Window
                Window.Current.Content = rootFrame;
            }

            if (rootFrame.Content == null)
            {
                // When the navigation stack isn't restored navigate to the first page,
                // configuring the new page by passing required information as a navigation
                // parameter

                var setup = new Setup(rootFrame);
                setup.Initialize();

                var start = Cirrious.CrossCore.Mvx.Resolve<Cirrious.MvvmCross.ViewModels.IMvxAppStart>();
                start.Start();
            }
            // Ensure the current window is active
            Window.Current.Activate();
        }

3. For Windows 8 - Add a views folder and a view - xaml.cs and .xaml based on BasicPage - this will add 5 files to the Common folder. 
  - Change the Common/LayoutAwarePage.cs inheritance to Cirrious.MvvmCross.WindowsStore.Views.MvxStorePage
  - Change the Common/LayoutAwarePage.cs - remove the OnNavigatedTo and OnNavigatedFrom handlers
  - Add some content for your Xaml - e.g. <TextBlock Grid.Row="1" Text="{Binding Hello}" />
  
5. For Windows 8.1 - Add a views folder and a view based on the BasicPage template
  - In the .xaml.cs - remove public NavigationHelper NavigationHelper and all referencing code
  - In the .xaml.cs - remove the OnNavigatedTo and OnNavigatedFrom handlers
  - Add some content for your Xaml - e.g. <TextBlock Grid.Row="1" Text="{Binding Hello}" />