Prioritization and scheduling of this bug is tracked on Mingle card https://mingle.corp.wikimedia.org/projects/flow/cards/224

Change 88683 had a related patch set uploaded by Legoktm:
Support global group change notifications

https://gerrit.wikimedia.org/r/88683

Re-setting to NEW - that patch is for bug 51541 not this.

I just looked into this. The reason why this is hard is that the Echo event occurs on the central wiki (metawiki in our case) but needs to be inserted into another wiki's database, which appears to be completely unsupported by Echo's infrastructure.

I suppose it would be possible to hack this in using cross-wiki notifications, but that would probably be very confusing to users.

If you create the notification on meta, then cross-wiki notifications will ensure that the user still sees it, but it will appear to come from meta, which may be confusing. It's probably better to find a way to get the target wiki to create the notification instead, maybe by queueing a job (I think a wiki can queue a job for a different wiki, right?) or with an API request or some other trick.

In T53540#3216533, @Catrope wrote:

If you create the notification on meta, then cross-wiki notifications will ensure that the user still sees it, but it will appear to come from meta, which may be confusing. It's probably better to find a way to get the target wiki to create the notification instead, maybe by queueing a job (I think a wiki can queue a job for a different wiki, right?) or with an API request or some other trick.

Yes, it's simple for a wiki to queue a job for another wiki: https://phabricator.wikimedia.org/diffusion/EMAM/browse/master/includes/job/MassMessageSubmitJob.php;391e1d5d3b022f610b2037effc04aaee97a58a3c$29 .