It’s hard to do that in a federated / decentralised system that does not guarantee message order and that every message is delivered like email.
Technically it would be possible to have a group with one admin, but it gets hard as soon as you introduce the option to promote other people to also be able to change permissions and settings. (and not all clients get the message of the promotion before the action the new admin took, so some clients would reject the action that the new admin took, because have not received the promotion message yet)
It would be easier to integrate sth like a mailing list api or bot where you can have special groups that run over a mailing list server and you configure the mailing list from inside of the DC interface via a seamless integration, but with pure email it’s close to impossible, unless you want to introduce a chat-multiverse like in a blockchain, but even then I’d doubt that it would work or be a good user experience so I think hosted/mailinglist groups are the way to achieve this.
Also see the other topics about group types on the forum:
- New feature: Group Types
- Public Group Chats possible?
- and some other topic that you can search for yourself if you want…