Indexing NAS with "mdutil -i on" with Sierra not working anymore
According to this support page by Qumulo, there is a fix, which basically consists of the following:


  To fix this issue, create the following directory as root:
  
  sudo mkdir -p /private/var/db/Spotlight-V100/Volumes/
  
  And then re-enable Spotlight indexing of that Volume:
  
  sudo mdutil -i on /Volumes/name_of_your_volume


I haven't tried it myself, but I thought it's worthwile to mention it here.