Since I started this thread, I thought I’d just weigh in and say that my request for hierarchical groups is still completely relevant.
The Bulk Invite to Group feature simply doesn’t come into play because in my case, I’m adding people to specific age-based groups and an overall group that encompasses all the age-based groups over a 4-month time frame as they register in another system.
I’ll see if my developer can automate the process this year, now that I know how utterly tedious it is to do by hand on a weekly basis.