For T279664 the plan was to use testwiki, test2wiki and mediawikiwiki as pilot deployments to test whether multi-DC is working. However, these wikis have a large number of completed or abandoned experiments in their configuration with the potential to obscure the results. For example, I tested Echo notifications, but I missed the fact that Echo is configured to use the job queue only on the three wikis mentioned above, so the real production code was not exercised.
As production test wikis, testwiki and test2wiki have the most value when they have a configuration matching the wikis we care about.
Removing experiments can also be justified in terms of reducing clutter and the size of the production configuration.