It would be nice to have the ability to notify users when new content has been published to a group that the users are a part of.
For example, if I overwrite a service to update it, or publish a new service and share it with a group, all the members of the group I shared the service with should receive a notification informing them of that update or new content that was published which they now have access to.
I think the best way to do this would be to just implement a checkbox in the ArcGIS Desktop Service Editor where you select what groups you want to share the service with, a simple "Notify Users" checkbox would be sufficient. AGOL/Portal would then need to interrogate the setting of this parameter and if True, give all of the users who are part of the groups the service is shared with some sort of simple notification badge or something like that to inform them.
Similar to the way AGOL gives you a notification when you've been invited to a group.
This idea has been marked as a duplicate of SIntroduce email notifications for ArcGIS.com group owners and members.. Please up vote the linked idea to show your support