The content of RadBackstageItem is not stretched within the available area in the content area of the RadRibbonBackstage control. There is a gap between the title bar of the RadRibbonView control and the top border of the content area.

This reproduces with the Material theme, but it is possible to appear also in other themes.

To work this around, you can extract the ControlTemplate of RadRibbonBackstage and re-order the layout in order to stretch the content in all the available space. Check the attached project.

Currently, the minimized content of the ribbon opens up in a Popup element which leads to issues when positioned between two (or more) monitors. Introduce a feature that allows the content to opens in an Adorner element. 

Setting the KeyTipService.AltAccessText attached property on a RadRibbonGroup element should display a keytip on the dialog launcher of the group, when the keytips are activated.

Currently, if the group is collapsed, you can expand it using its AccessText. However, in this case the keytip of the dialog launcher is not displayed.

To work this around, subscribe to the Loaded event of RadRibbonGroup and set the KeyyTipService.AccessText property directly to the RadRibbonButton representing the dialog launcher.

private void RadRibbonGroup_Loaded(object sender, RoutedEventArgs e)
{
	var group = (RadRibbonGroup)sender;
	var button = group.ChildrenOfType<RadRibbonButton>().FirstOrDefault(x => x.Name == "DialogLauncher");
	if (button != null)
	{
		KeyTipService.SetAccessText(button, "D");
	}
}

Implement keyboard navigation for the items in the ApplicationMenu - through arrow keys for example.

Workaround:
In the Loaded event of the RibbonWindow, use the Telerik.Windows.Controls.RibbonView.Shell.WindowChrome class to get the current window and set its ResizeBorderThickness property to 0. 

public MainWindow()
{
    InitializeComponent();
    this.Loaded += MainWindow_Loaded;
}
 
void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
    Telerik.Windows.Controls.RibbonView.Shell.WindowChrome chome = Telerik.Windows.Controls.RibbonView.Shell.WindowChrome.GetWindowChrome(this);
    chome.ResizeBorderThickness = new Thickness(0);
}