It is recommended by Microsoft to migrate to DFSR from FRS for SYSVOL replication on domain controllers. It is common for old domains to not have had the migration preformed since it requires a manual upgrade by an administrator. Windows Server 2016 is the last version of Windows that will support FRS, eventually all domains will need to upgrade to DFSR so an alert for which domains have not been migrated will be beneficial. Since AD Recycle Bin and end of life forest or domain levels are detected and alerted on adding a SYSVOL DFSR check will add to the existing domain health checks.