Obviously the memberslist.html would have to be changed, and space made to display a - possibly long - list.
modules/Members_List/index.php would need to retrieve user_group_cp and user_group_list_cp as part of the cms_users tuple access.
This would give you access to the group numbers, so the names of groups would have retrieved in a similar fashion to how it's done in modules/Groups/index.php (following the last option - under else - in the module).
But in between you'd have to implode the list of group numbers to get the list in array form.
Lot of work, and a little more SQL run time, for how much benefit?
For general use you'd also have to consider display by group type vs. membership. Admin would probably want to see all, but wouldn't want members to see Hidden groups, eg.
Thanks lb, I'll look at the groups index page and see if I can do it. I have groups for a school website and I'd like an easy way to show in the members list who is a teacher and who is on the committee...
Server specs (Server OS / Apache / MySQL / PHP / DragonflyCMS):