Cross wiki notifications will be released by default on *May 12 at 23:00 UTC*.
Documentation has been updated and need translations: https://www.mediawiki.org/w/index.php?title=Special:Translate&group=page...
During the beta phase, the cross-wiki notifications feature was enabled by over 18,000 accounts across more than 360 wikis. We receive great feedback from a lot of very happy users. After that 3-months long beta period during which we made adjustments, that feature will be released by default on May 12 at 23:00 UTC.
Users who don't want to receive cross-wiki notifications can turn them off at individual wikis. More information is available on the documentation https://www.mediawiki.org/w/index.php?title=Help%3ANotifications%2FCross-wiki. The talk page https://www.mediawiki.org/wiki/Help_talk:Notifications is still open for any questions or feedback.
Do not hesitate to spread that information on your wiki! :)
Thanks, Benoît