You should be able to prevent the horizontal/vertical overlapping of routed connections . This way the connections should be easier to differentiate.

To better differentiate connections, users might:

            --- use labels on the connections

            --- use bezier connections

            --- use different colors for different connections

            --- use more custom connectors and attach the connections to not used connectors

            -- use AStartRouter instead of the default one (Grid Router)

Currently large diagrams are hard to export with good quality because of the memory limitation in WritableBitmap when the DPI is increased.

 -- One option is to use BitMapCacheBrush (discussed here http://www.telerik.com/forums/low-resolution-using-exporttoimage-on-big-diagram)

 -- Another option is to export multiple images of the diagram which cover it all. Then possibly combine these pictures into one.

 -- Also , you can try increasing the operating memory of your Visual Studio

Ability to export a diagram to PDF.

Implement support (or extensibility) for printing the whole diagram in a single page.

Currently the Bezier Connections Start,End Points and the two editing points are created in a common Canvas. There is no mechanism to hide the editing points but show the start and end point.
Note: Currently there's a way to hide editing or intermediate points - you'll need a style and a converter. We've added a new SDK example (HideBezierHandles) demonstrating this.

ManipulationAdorner (including Rotation thumb, resizing thumbs) should not be zoomed along with the shape.

Diagram Shapes' property is bound to property from the ViewModel.
Case 1) Using GraphSource =>Shapes DataContext is automatically apllied. GraphSource is set to null or changed.
Or
Case 2) Not using Graphsource. Shape's DataContext is set manually (in code behind). Diagram.Clear() is invoked.

Result: Binding Expression erors in Output indicate missing properties - these are bound properties of the shapes.

Inherit RadDiagramConnector and add it to a Shapes' Connectors collection. Copy / Pasting (or other serialization / deserialization action) the shape creates RadDiagramConnector, not the custom type of connector.

Allow the user to customize the caps (SourceCapType and TargetCapType) of the connection.

Exposed are  two new virtual methods in the RadDiagramConnection - CreateSourceCapGeometry and CreateTargetCapGeometry

Available in Q1 2015

In data binding scenarios these propeties are not updated automatically. Currently if you want to bind the StartPoint and EndPoint properties of the RadDiagramConnection you will have to update new position of the connection manually. This can be done in the PropertyChanged event of the connection. In the Handler you can cast your connection to IConnection and call the Update() method, if the e.PropertyName holds the property that you change.

Will be available in Q1 2015 Release.

Should be able to override the AbsolutePosition and the Offset of the connector. Should be able to specify absolute position manually, not only relative.

Should be able to provide template for its visual representation.

Fixed in LIB version: 2014.2.0914

Expose a property to set the DiagramBehaviors.TextWrapping attached property on a diagram level

-- 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.

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

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

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

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

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

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.