I'm surprised this new functionality has not been posted here yet. This seems like a BIG deal and something many have been asking for, for a LONG time. Even before groups existed this was a common third party ask for SharePoint sites. I just hope it doesn't require an E5 license or something ridiculous when it moves out of preview.
https://blogs.technet.microsoft.com/enterprisemobility/2017/08/09/automated-expiration-for-office-36...
