Currently when you have null value in a cell, RadPivotGrid considers it as 0. This way when you apply some Aggregate Functions, like Average for example, the result may not be as expected. For example if you have the cells 10, null, 10 RadPivotGrid will show as total the value 6.67 (for Average function). You should be able to exclude null values, so the value 10 will be shown as average for the mentioned cells.

Available in the 2016 R2 release.

Similar to Excel - RadPivotGrid could have an area, where you can select some filter/group descriptions.

Users should be able to select individual or multiple cells of RadPivotGrid.

Available in the 2016 R3 Release.
Please take a look at our help article for more information: 
http://docs.telerik.com/devtools/wpf/controls/radpivotgrid/features/selection

As a user I want to hide the Grand Totals for specific groups.

I would like RadPivotGrid to sort the dates defined in OLAP Cube as dates, for example:
-Week 1 -Week 2 -Week 12   Instead of the current sorting: -Week 1 -Week 12 -Week 2

Implement functionality to show a break down of items that aggreagate to current cell.

Available in the 2017 R1 Release (2017.1.117).
For more reference you can check the following help article: http://docs.telerik.com/devtools/wpf/controls/radpivotgrid/features/localdatasourceprovider/drilldown

If a group has only one item in it, I only want to show the total row and not being able to expand it.