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).
- 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)).
- Store the date each beta feature was launched (may very by wiki) in config.
- 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.
The old code should be removed, because it causes bugs like T164118: Can't turn off "New filters for edit review" if "Automatically enable all new beta features" is on.