I actually got it several days ago by putting USA English at the top of the languages in main settings, then going into the apps settings and deleting the Google app search data. Assistant then showed up and has been working ever since even after changing back to UK English.
However at that time it didn't work on my wife's 6p but took a few days trying for it show up.
However at that time it didn't work on my wife's 6p but took a few days trying for it show up.