Include the Show more/fewer and add/remove buttons functionality in the bottom menu.
Properties that get the ActiveItems' Count and MiniizedItems' Count also needed.

Collapse bar to a slim version, reorganizing the icons to be vertical without description but with hover over descriptions.

Approach to implement:

RadOutlookBar is minimizable by default.
Descriptions of the minimized RadOutlookBarItems can be achieved in WPF via:

<Style TargetType="telerik:RadOutlookBarItem" BasedOn="{StaticResource RadOutlookBarItemStyle}">
    <Style.Triggers>
        <DataTrigger Binding="{Binding RelativeSource={RelativeSource AncestorType={x:Type telerik:RadOutlookBar}}, Path=IsMinimized}" Value="True">
            <Setter Property="ToolTipService.ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=Header}" />
        </DataTrigger>
    </Style.Triggers>
</Style>

or by adding this trigger to the RadOutlookBarItem's ControlTemplate.Triggers

There should be a way to set horizontal orientation for the items of the OutlookBar.

Create integration example with TransitionControl.

TabIndex/Tab navigation is not working inside OutlookBar.

Add a section, separate from Content area

Event when dragging the horizontal splitter

Add StyleTypedProperty to MinimizedArea to aleviate editting the item container style of the MinimizedAreaItem.

Implement "Add or Remove Buttons" functionality as in MS OutlookBar.
http://www.telerik.com/ClientsFiles/170274_fortelerik.jpg

Allow the user to manually set the position of the OutlookBarItem : ActiveArea, MinimizedArea or OverflowArea

There should be a way to swtich items and navigate the content easily using the keyboard only.