My back brain just won't let this go, but I'm splitting it off into its own thread.
It seems to me that there are two (as in many things in life) main ways of viewing 'groups': OWNED and ADMINISTERED (or choose the words of your preference).
An OWNED group is one that is tightly controlled by the OWNER. An example is a business that wants a 'support' group, but wants to retain absolute control over the group. This type of group is like a "living room" (to use an already coined phrase :-), and the walls, floor and ceiling can be redecorated or burned to the ground at the whim of the OWNER.
An ADMINISTERED group is one that is more loosely controlled by (usually) multiple administrators. An example is a hobby group where all the members share a common interest and want to have a voice in the running of the group. This type of group is like a "town square" where everyone is welcome and invited to build a home or set up shop, and the decisions regarding the group are made more democratically, first by the ADMINISTRATORS, and they are guided by the will of the group as a whole.
One might consider that these two could be merged into a single concept, but doing so raises a number of messy issues. Here are some of the differences in behavior that come to mind, but I know this is not an exhaustive list:
1) The OWNER generally wants to be able to add, modify, and delete content, sub-groups, the group, etc., at will, regardless of the wishes of the group membership, whereas in the ADMINISTERED mindset group, the members want a say in what happens in and to the group.
2) An OWNER may want to make sure that, regardless of what may happen to them, the group will continue (or not) according to their wishes, whereas members of an ADMINISTERED group want to make sure that the group will continue regardless of the wishes of the ADMINISTRATORS.
3) In cases of ToS violations, the OWNER is ultimately responsible for dealing with these and must answer to Groups.io appropriately. If the OWNER fails to do so, the group may be deleted or handled in whatever fashion Groups.io wishes. For ADMINISTERED groups, the ADMINISTRATORS (who answer to the group's members) are responsible for dealing with these problems and (perhaps) FILES and non-POLL messages can be blocked by Groups.io until the problem is dealt with or new ADMINISTRATORS are appointed by the membership (via POLL) to deal with the issue.
4) For OWNED groups, any OWNER may delete the group at any time. For ADMINISTERED groups, ALL administrators must agree before a group may be deleted.
5) For OWNED groups, if the OWNER(s) disappear for an extended time without an 'heir', there is no mechanism for reviving the group under new leadership. For ADMINISTERED groups, if all administrators disappear, the membership can petition Groups.io to re-administer the group (via whatever means, possibly message-ing the group for volunteers, then running a poll for election). This has long been an issue on Yahoo Groups, which they've failed miserably to deal with.
6) For OWNED groups, a single OWNER may wish to maintain absolute control of a group, but be able to designate an heir (or an ordered list of possible heirs) for their group should they disappear for a specified time (1,2,3,6,12 months?), or they may wish to have the group automatically deleted if they disappear for the specified time. Heirs might be supported for an ADMINISTERED group, but not really needed given the ability to "re-administer" a group.
I'm sure there are many other differences and situations, but I'm not attempting to be exhaustive about this, but rather to paint a picture of the different mindsets about "group ownership," and why a single method of handling these may not be the best. What's good for the goose is not necessarily good for the gander.
There would have to be a mechanism for switching a group between OWNED and ADMINISTERED, easily done in the SETTINGS, but ALL owners or administrators would have to agree before the change could be made. This could easily be handled by having a 'master' OWNER/ADMINISTRATOR setting and individual settings for each OWNER/ADMINISTRATOR. For an OWNER group, all OWNERS would have to change their setting to ADMINISTRATED before the master (effective) setting would change. All ADMINISTRATORS would have to change their setting to OWNED before the master setting would change.
Were Groups.io (i.e., Mark :-) to decide there was validity in this idea, I would imagine that all CURRENT groups would be OWNED initially by their current OWNERS, and then each group (should the OWNERS of the group wish) could change to ADMINISTERED as/when they wished.
It would be important to note the type (OWNED/ADMINISTERED) of the group on the group's home page and to clearly explain the ramifications of this when a member joins Groups.io and/or individual groups so that the members' mindsets and expectations for the group are set properly.
Obviously, Groups.io is an OWNED group :-), so all we members can do is suggest and request.