User blog comment:Brandon Rhea/How we're testing the fandom.com domain migration/@comment-33815196-20181005171901/@comment-20644-20181005185528

We can't offer an opt-out for the test. We chose a number of wikis of different sizes and different verticals (like movies, games, TV, etc) so we'd have a comprehensive set of domains and keywords to study. Removing any of them at this point would negatively impact the study.

Keep in mind too that by early next year, likely January, the wiki would be on fandom.com instead of wikia.com anyway so all this means it that it's happening a bit earlier for some wikis.