For those looking for information of ReFS upgrade:
From Windows Server 2012 R2 (ReFs 1.2) to Windows 2016: ReFS is NOT upgraded (not by an in place upgrade and not by presenting an existing ReFS 1.2 LUN to a Windows Server 2016). Those already using ReFS or thinking about using ReFS on Windows Server 2012 R2 now for "future proofing" should know they'll have to do a data migration. You can keep your data on ReFS 1.2 and it's readable by Windows Server 2016 but you wont gain the great capabilities you're after.
An upgrade from Windows Server 2016 TPv5 (ReFS 3.0) to Windows 2016 RTM (ReFS 3.0 or 3.x?) is supported by MSFT. But just like Veeam B&R 9.5 Beta it's all just for testing & evaluation ... these are not RTM ready products.
I'm quite enthusiastic about it so I hope to move fast come RTM I have one repository at the ready with a LUN to be formatted with ReFS v3
That's my understanding for the moment.