What problem does this feature solve?

The 5.2.0 feature of Universal Transition works great for drilling down 1 level. I am trying to create drilling down to multi-levels and can't figure out how to do it. My idea was that the groupId from the previous level becomes dataGroupId of the current level and the current level will use the itemGroupId for the groups of the current dataset. However, specifying itemGroupId in the second level completely stopped the animation.

What does the proposed API look like?

I think there should be a way to distinguish between the group a data item belongs to from the drill-through group and also a group it forms for further drill-down.