Thanks for the request. Currently there is a way to set this property through powershell for groups, but it only works for users in OWA. We have this in our plans for Outlook desktop as well and will be working on it.
Thanks.Roger M Cotrofeld Jr commented
We specifically need this function for departmental groups within our tenant. Each department wants a group calendar to manage a time off calendar, but they only want owners of the group to be able to add items as a method of scheduling only approved absences. They have been doing this through personal shared calendars previously, but since the O365 implementation when the account owner leaves the calendar goes away with their license removal.