Spotlight borked after macOS Sierra update
Did you reboot after #4 above? I think that should work... If not this may help:

sudo touch /.metadata-never-index


Reboot...

sudo rm /.Spotlight-V100/VolumeConfiguration.plist
sudo rm /.metadata-never-index


And reboot again. You can try this for every volume.

See also: http://www.filetypehelp.com/purpose-files-metadataneverindex-file-extension/