Currently, to modify the background color of this element, the default control template of the GridViewCell element needs to be extracted, and the VisualState with x:Name="Highlighted" would need to be customized.

We could include an API for modifying the background color of the HighlightTextBlock element, when it is highlighted.

Calling the BeginInsert() method of RadGridView, adds a new row at the bottom of the items and scrolls to the newly added row. However, if the vertical scrollbar is not visible and the newly added row makes the viewport so big that the scrollbar should display, the row gets clipped. Also, the vertical scrollbar that was just added is not scrolled to the bottom, which is actually why the row is clipped. Each next insert (after the scrollbar gets visible) will display the added row properly.

To work this around, you can scroll the vertical scrollbar manually to bottom. 

private void BeginInsertRow()
{
	var scrollViewer = this.gridView.FindChildByType<GridViewScrollViewer>();
	bool requestScrollToBottom = false;
	if (scrollViewer.ComputedVerticalScrollBarVisibility == Visibility.Collapsed)
	{
		var panel = this.gridView.FindChildByType<GridViewVirtualizingPanel>();
		var sumHeight = (source.Count + 1) * this.gridView.RowHeight;                
		requestScrollToBottom = sumHeight > panel.ActualHeight;                
	}
	this.gridView.BeginInsert();

	if (requestScrollToBottom)
	{
		scrollViewer.ScrollToBottom();
	}            
}

Add a textbox which allow search and filter functionality for the distinct values in the FilteringControl of RadGridView.

In the meantime, you can check the attached project that shows one way to achieve this.

radGridView has a feature to provides a suggest and append feature.  Currently, there is the ability for the end user to inadvertently close this window.  Please provide the opportunity via a property to disable the ability to close the search window.  (currently, I am hooking the SearchPanelVisibilityChanged event, and forcing showSearchPanel = true at all times.

Scheduled for: 
The exposed property (SearchPanelCloseButtonVisibility) will be available with LIB (version 2018.3.1210) published on Monday, 10-th December, 2018.