It would be great to have a flag on the table indicating if any of the grouped rows are open (either binary, or more detailed if there are multiple groups).
For example, I have a table that displays more granular account data based on a row being selected in another table. I group that account data by year, by default, which is great because I can see the aggregations of a bunch of values very cleanly. When I expand the year, I can see details of the records, with things that don't aggregate well, like dates, names, tags etc.
If I could tell if the row was open/closed, I could leverage the hidden prop on the columns to hide the non-aggregable rows when they serve no purpose.
Thanks for the +1, @macphreak! I wish I had a more exciting update, but it looks like this is in our backlog currently, so we don't have a timeline yet. I will follow up here if this gets prioritized internally