It was mentioned in the 70-411 Distributed File System (DFS) episode that FRS is enabled by default for legacy OS support. However, if your organization has only deployed Windows Server 2012 Domain Controllers (DC) and file servers, will DFSR be utilized or does it still default to FRS and require migration?
Microsoft Windows Server 2012 - Distributed File System
It depends on the domain functional level. If you installed Windows Server 2012 on your first domain controller, but chose 2003 domain functional level, FRS would be used for backwards compatibility. As long as you chose 2008 or higher domain functional level, DFS will be used for SYSVOL replication, no migration necessary.