Research and improve the virtualization performance. Currently, the virtualization in the diagram creates containers for all shapes and sets the Visibility of the containers outside of the viewport to Collapsed. This saves from the layout and rendering performance, but it is not optimal. Consider implementing a standard virtualization mechanism which adds containers in the visual tree only for the shapes within the viewport.

User scenario:
When zooming out on more than 500-600 shapes and then panning, if telerik:DiagramSurface.IsVirtualizing="True", the performance is slower. When virtualization is off, the performance is a little better.