This feature is under review for Enterprise Edition.XANi commented
It would be nice to have ability to have a channel where only specific person (either a group or say just Team Admins) have ability to speak.
We have few channels that are used for annonucements (like one with food delivery, other with builds etc) that are subscribed by most of the employees, but people still have conversations in it, spamming almost everyone in company with them
Thank you for this feature idea! We have started to work on this feature.
Also note that we have experimental system-wide default theme settings: https://docs.mattermost.com/administration/config-settings.html#theme-settings-experimental.XANi commented
It should be extended to notification preferences as well. Defaults ("notify and email about everything") can be very spammy with bigger teams and having to teach every user how and where to change it (including ones that are not that technically literate) is a lot of work