Refers to "Automatically enable all new beta features"
From bug T62748.
> However, the current code will only enable the new betafeatures when the user visits Special:Preferences, or whenever the 'GetPreferences' hook is run (API's action=options I think).
Needs to handle metrics properly (see comments).
1. Keep track of date "Automatically enable..." was set to "yes" in a hidden preference/somewhere (when you turn this off, it clears the date and stores all the existing enabled Beta Features as explicitly on (since the default will then flip).
2. Store the date each beta feature was launched (may very by wiki) in config.
3. Use UserGetDefaultOptions. If "Automatically enable" is on, set the default to "enabled" for any Beta Feature that was launched after the "checkbox yes date" (see #1). Otherwise, the default is "disabled". Either way, you can override the default by saving preferences at any time.