Eternally stalled. Would need input from the SRE Infrastructure, Traffic, and Observability teams, the Web team, the Performance team, and others.
T69703: Change MediaWiki default thumbnail size to 300px based on user behavior suggests that we change the default wiki thumbnail size to 300px width, based on user settings data, for all Wikimedia wikis as well as for the MediaWiki software itself. Copying here for that part of the change.