I didn't make a sencha architect component for this but I have finally managed to implement the columns expand/collapse feature.
A drill down plugin could be easily implemented. Double click a cell in this example and you'll see how many records were used to aggregate that cell value: http://www.mzsolutions.eu/mzPivotGrid-configurator.html
I would like to point out that the folks that are supporting this have been very responsive to questions, and integrating feedback. They have already included things that were asked for (in days).
In my applications, it is very commonplace for user's ability to multi-sort, multi-group, and interact with the grid details.