Hopefully I can explain this in a way that makes sense, and if this is already implemented and I simply haven't found it, all the better ...
One of the 'hitches' that I am running up against with HierarchicalTable is that I have some cases where I have a long list of items in a table, and I want to have them all expanded; for example, to show a block of text providing extended information regarding the table row. Since HierarchicalTable must have a distinct component for each expanded row, this can start to consume a lot of memory and slow things down.
What I would like to see is a variation that treats the child components in much the same way the table treats a cell; the child component is actually a renderer that is passed some row specific parameter to update its display for a specific row, and the same actual component can be reused for every row. This could then be extended further to allow for an 'editor' component (again, as the table does) when a particular expanded child is selected.
I don't know that this would work so well for the Hierarchical nature of HierarchicalTable, for displaying a little extra information with each row, it seems like it could be much more efficient.