Some users have activities to cross-wikis, but in this time, Echo only works in local wiki. So users could not receive other wiki's notification in their home-wiki. We already have email notification, but I think global echo notification is also good for better experience.
URL: https://www.mediawiki.org/wiki/Requests_for_comment/Cross-wiki_notifications
See Also: T3066: Please add cross-wiki talk page notification.
(In reply to JuneHyeon Bae (devunt) from comment #2)
Legoktm: Is there some in-progress development code?
Not any that I'm aware of.
I seem to recall me and Kunal discussed this back in January and realised it would involve dealing with things like checking revdel flags across wikis, among other things
Let us assume that some user is highly active on two projects (A and B), but his home-project is A. So it would be nice, that on A he could get all project notifications, except for B (so the notification bar isn't so backlogged).
Would it be possible? Of course, this could be implemented in later, not together with cross-wiki notifications itself.