Can you raise the domain functional level to windows server 2016 and have DFS running on windows server 2012 r2?
Solution 1:
It shouldn't as the two compatibility modes are separate (DFS and AD that is). We did the same transition from 2012 up to 2016. If you leave the DFS server in 2008, it should still work with a 2016 Domain Level. Just do not change one of your DFS servers to a higher compatibility mode without doing the other.