An update before the weekend: We've found that the upgrade script causes some slowness, so it's currently only running at the quietest times of the day to reduce the overall server load. This has meant the process is taking much longer than we initially planned. There are about 30,000 wikis (out of 190,000 or so) that still need upgrading. These are often the more active ones, so we still have a way to go! The quick way to check if a specific wiki has been upgraded is to look at the top Wikia bar - if it's smaller and higher than before, then the wiki is on 1.16 (see Community Test for example.
We'll be upgrading more wikis over the weekend, so please bear with us if you see any oddities or slowness - thanks all.