There should be annotations (comments) system built into the framework:
€¢something like Word where one can add to a word a note
€¢something like Excel with its comments bag
€¢something like Workflow Foundation where every shape has a popup bag

A possible workaround is to use an attached property. Basically, we've added ConnectionPointsProperty in AttachedProperties class and added binding to this new property in the style of the connection.

public class AttachedProperties
    {
        public static RadDiagram Diagram { get; set; }

        public static readonly DependencyProperty ConnectionPointsProperty =
           DependencyProperty.RegisterAttached("ConnectionPoints", typeof(List<Point>), typeof(AttachedProperties), new PropertyMetadata(null, OnConnectionPointsChanged));

        public static IEnumerable<Point> GetConnectionPoints(DependencyObject obj)
        {
            return (IEnumerable<Point>)obj.GetValue(ConnectionPointsProperty);
        }

        public static void SetConnectionPoints(DependencyObject obj, IEnumerable<Point> value)
        {
            obj.SetValue(ConnectionPointsProperty, value);
        }

        private static void OnConnectionPointsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var connection = d as RadDiagramConnection;
            var connectionPoints = e.NewValue as List<Point>;
            if (connection != null && connectionPoints != null)
            {
                for (int i = 0; i <  connectionPoints.ToList().Count; i++)
                {
                    connection.ConnectionPoints.Add(connectionPoints.ToList()[i]);                 
                }
                connection.IsModified = true;
                (connection as IConnection).Update();
            }
        }
    }



  <telerik:RadDiagram.ConnectionStyle>
                <Style TargetType="telerik:RadDiagramConnection">
                    <Setter Property="ConnectionType" Value="Polyline"/>
                    <Setter Property="local:AttachedProperties.ConnectionPoints" Value="{Binding MyConnectionPoints}"/>
                </Style>
            </telerik:RadDiagram.ConnectionStyle>

Implement "Item to Item Snapping" during item resize operation.

Add ContainerShape ContentTemplate and ContentTemplateSelector properties in RadDiagram

This is reproducible only if you set the RotationOrigin property to a value different than (0.5,0.5). Also, the rotation angle is wrong only on the first call of the Rotate() method of the service. 

To work this around you can create a custom RotationService and override its CalculateRotationAngle() method where you can calculate custom angle. 

http://docs.telerik.com/devtools/wpf/controls/raddiagram/features/services

https://github.com/telerik/xaml-sdk/tree/master/Diagram/CustomServices

-- Add ClearCache method to clear the undo-redo dictionaries used internally

or

-- make the undo-redo dictionaries auto clear when undo-redo stacks are cleared

Available in LIB version: 2016.3.1114
Clear method of Diagram's UndoRedoService now clears the UndoRedo internal cache automatically.  
What's changed ? The public interface IDiagramContainerGeneratorInternal interface now adds ClearCache method:
A) this.Diagram.UndoRedoService.Clear(); will clear the internal undoredo cache which stores model-container relations. Also this will clear the undo/redo command stacks.
B) this.Diagram.ContainerGenerator as GenericContainerGenerator<RadDiagramItem>).ClearCache(); will clear ONLY the undoredo cache.

Be able to pre-select, printer, page size and page orientation in the RadDiagramPrintPreview. By default, RadDiagramPrintPreview set the printing orientation in landscape even if we created a diagram in portrait. 

Users need to create custom mouse tools and set them as ActiveTool of the RadDiagram.

When user hovers a connector and pastes a connection, the pasted connection should be attached to the hovered connector.

You can check the Diagram SDK sample in GitHub - "PasteOnMousePosition" whic demonstrates this functionality.

https://github.com/telerik/xaml-sdk/tree/master/Diagram/PasteOnMousePosition

We are marking this feature request as declined - the code in the SDK sample is the preferred way to go instead of built-in feature.

Connection Bridges Greatly Degrade Performance. Iven if there are no crossings, performance is very slow.
 In some scenarios empty spaces on the connections are observed even if there are no crossings.

The fix will be available with Q1 2015 Release.

Introducing Page size (A4, etc) concenpt and vertical and horizontal rulers

Add spell checking to the shape and connections, while editing

Select some color from settings pane for some shape.
In order to use the same color for other shape you need to deselect this color on your own (by selecting other color) and then select it again.

Available in LIB version: 2014.3.1117

Implement functionality that notifies the user when a shape is dragged out of a container.

Users should be able to easily customize the Pan operation of the diagram.
Update: With Q1 2014 you'll be able to customize all the diagram tools

In some cases when there are no crossings, empty spaces can be observed on the connections.

The fix will be available with Q1 2015 Release.

When a RadDiagramItem is deserialized, some of its properties receive local values. This is why if you have applied style setters on these properties, the value applied by the style setter is no longer used.

Currently, the print preview control provides only options for the current printer, the page orientation and the page size . Include the following options too:

 - Paper Format (Lettre, A4, etc.)
 - Paper Orientation (Portrait or Landscape)
 - Number of copies (1, 2, 3, ...)
 - Print Color Settings (Colors or Monochrome)
 - Margins
 - Resolution (DPI based on the capabilities of the printer)