Sometimes the application never loads the requested dlls' content.

Convert the interfaces and base classes (i.e. non UI specific logic) to a portable library.
We intend our solution to share Models and View Models between WPF and Silverlight (and more in the future). Our intention is to use Portable Libraries to achieve this. The biggest issue we have is down to the Telerik assemblies. Classes and interfaces that are shared between WPF and Silverlight could/should be in a PCL assembly.

Optimize binary and text resources like fonts, images...etc. Especially for the RichTextBox.

Add support for DataVisualization assembly or prompt message that we don't support it right now.

Support PRISM / MEF in Xap minifier.

In UIElementExtensions, IsAncestorOf crashes when the element parameter is of type Hyperlink.

The xaml team recently reviewed the status of this issue and won't be addressing it in future. 

The LocalizationManager doesn't apply the ResourceKey if the Content/Text properties are defined in XAML between the opening and closing tag of the control - for example Button or a TextBlock control.

Support Documents (RichTextBox) assemblies

Implement a command line version which can be integrated with TFS.

Annotations are not positioned correctly, when the vertical scrollbar is visible.

The fix is available in LIB Version 2014.3.1319.

Same as in WPF

Same as WPF suggestion

Summer, Office_Silver, Office_Black Themes cannot be minified , after loading they dissapear from the "extracting" grid

XamlParseException when minifying the XAP

Telerik.Windows.Controls.Charting.dll cannot be minified

The MaskedInput controls cannot be extracted from the Telerik.Windows.Controls.Input.dll

Create FileThumbnail control:
I would love to have an easy way to display the thumbnail preview of a file. The Windows Shell does it, but the pInvoke code required to make this work is excessive.
Something like this:
http://stackoverflow.com/questions/1439719/c-sharp-get-thumbnail-from-file-via-windows-api
Perhaps a "RadFileThumbnail" control?
The Windows API Code Pack for Windows 7 has something like this, but you lock yourself into Windows 7 by using it.
http://archive.msdn.microsoft.com/WindowsAPICodePack