I would be excited by having the ability to shut down external ListServ systems, because the Exchange transport servers would handle DL expansion, including members not in AD, and use a sharepoint website as the repository and even message clearing house.
Having to use an external system for List management seems to be so redundant these days, but Exchange today cannot provide all the features they do w/o third party add-ons which essentially are stand alone anyway.
It would also be nice to have the ability to se an Out of Office, and have that temporarily exclude you from non-mandated DLs. So mandated DLs would still come to your mailbox, but less important ones were temporarily unsubscribed.