MergedCellsStyle and MergedCellsStyleSelector properties will be available with Q2 2016.

See this thread for more info:
http://www.telerik.com/forums/alternaterowbackground-doesn't-merged-with-rowstyle

It's  really common scenario, because a standard WPF DataGrid works like this.

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.

Especiall for wide lists it would be very helpful to be able to zoom in and out of a RadGridView, in order to see more or less columns. 

Also see: http://www.telerik.com/forums/scaling-of-radgridview-content

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.

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();
	}            
}

As a user I would like to have Unfocused state for selected GridViewCells when SelectionMode="Cell". 
Similar to the Unfocused state for selected GridViewRows (you can check this article as a reference: http://​www.telerik.com/help/wpf/gridview-selection-unfocused-state.html).