In the default control template of the RadSlider, the Track element is represented by a ContentControl control. When using the Xaml version of the assemblies, it would require extracting the TrackStyle, in order to base the custom one on it. An alternative would be to use the ChildrenOfType method to retrieve the ContentControl with x:Name="Track" and apply the needed modifications.

Both of these approaches could be a bit overwhelming when only the Width/Height properties of this Track element would need to be updated.

We could expose additional properties for changing the Width/Height values of this ContentControl (x:Name="Track").

Currently hiding certain ticks requires custom empty tick template or custom ticktemplate selector. When resizing such slider labels get overlapped because tick panel reserves space for the ticks - to preserve the proportions between tick values.

So user needs to use Canvas in the datatemplate of the tick.

The idea of this feature request is to somehow allow such feature out of the box with eventually additional property / behavior / built-in selector etc.

Wokraround: Set the Selection property in the constructor of the window using the SelectionRange<T> struct.

public MainWindow()
{
    InitializeComponent();
    this.radSlider.Selection = new SelectionRange<double>(11,16);
}

This is reproducible when the deferred dragging is enabled and the slider is defined in a template (DataTemplate or ControlTemplate). The selection values are correct, but the UI of the selection is not properly updated. 

To work this around you can subscribe for the Loaded event of slider and reset its IsSelectionRangeEnabled property.

private void RadSlider_Loaded(object sender, RoutedEventArgs e)
{
	radSlider.IsSelectionRangeEnabled ^= true;            
	radSlider.IsSelectionRangeEnabled ^= true;            
}

When you have set the value of the RadSlider to the maximum available and have placed the control within another element, lowering the width of the parent control does not cause the RadSlider to shrink as well.

Add possibility to input value like in the sliders from MS Expresion Blend 's ColorPicker

Implement Free/Lock/Push Thumbs interaction Modes like the ones in the Telerik RadSlider for Asp Ajax
http://demos.telerik.com/aspnet-ajax/slider/examples/thumbsinteractionmode/defaultcs.aspx

Mechanism to allow/force a refresh/rebind of the data template for the ticks needed

Add PreviewSelectionStartChanged, PreviewValueChanged and PreviewSelectionEndChanged.

Among with the minimum and the maximum, an allowed minimum  and alllowed maximum are needed to limit the sliders` selection range

Notification when reaching a tick.

Implement separate templtes for Top/Left and Bottom/Right ticks.

Add the ability to align the RadSlider ticks when they are used in custom TickTemplate. The ticks are currenlly always top/left aligned depending on the slider orientation.

Ability to snap the slider only at particular ticks

Currently, the containers for the ticks are generated and added in the visual tree even when the TickPlacement is set to None. Think of an improvement so that in this case the ticks are not added in the visual tree.

Expose an easier approach for styling the buttons that are placed over the slider's track. For example Style properties. Those RepeatButtons have their x:Names set to "LargeIncreaseHandler" and "LargeDecreaseHandler". 

Currently, in order to modify their appearance (like Background for example) you will need to override the entire ControlTemplate of RadSlider.