Change 62193 had a related patch set uploaded by Matmarex:
Fire Echo event when revision is rejected

https://gerrit.wikimedia.org/r/62193

Change 79775 had a related patch set uploaded by Matmarex:
Fire Echo event when revision is approved

https://gerrit.wikimedia.org/r/79775

(The first patch it actually Krenair's, I just linked the bug.)

Change 62193 merged by Aaron Schulz:
Fire Echo event when revision is rejected

https://gerrit.wikimedia.org/r/62193

Change 79775 abandoned by Matmarex:
Fire Echo event when revision is approved

Reason:
Somebody who knows at least one of the extensions should implement this. I give up.

https://gerrit.wikimedia.org/r/79775

There's an In-depth explanation from Atlasowa at https://www.mediawiki.org/w/index.php?title=Extension_talk:Thanks&diff=prev&oldid=686945#Early_thoughts

(and reminders/nudges/summaries at https://www.mediawiki.org/wiki/Talk:Echo_%28Notifications%29#Before_deployment_on_deWP_32656 and at https://en.wikipedia.org/wiki/Wikipedia_talk:Notifications#New_notification_.22gesichtet.22_needed_for_deWP.2C_plWP.2C_ruWP.2C_arWP_etc )

Prioritization and scheduling of this bug is tracked on Mingle card https://mingle.corp.wikimedia.org/projects/flow/cards/229

Change 79775 restored by Legoktm:
Fire Echo event when revision is approved

https://gerrit.wikimedia.org/r/79775

Change 79775 abandoned by Bartosz Dziewoński:
Fire Echo event when revision is approved

Reason:
I'd love it if someone revived this, but I won't anytime soon. Please resubmit as a new changeset in that case.

https://gerrit.wikimedia.org/r/79775

What is the plan ahead here? Is legoktm still the correct assignee, and does somebody plan to work on this soon (as it was set to high priority and ASSIGNED status)?
A status update would be welcome.

Note that there is related discussion in https://meta.wikimedia.org/wiki/Talk:Flagged_Revisions#Ignored_bugs_on_FlaggedRevs_for_stats.2C_.22gesichtet.22-notifications

Sorry, nope I don't plan on working on this anytime soon. https://gerrit.wikimedia.org/r/79775 is a good place for someone to start if they want to, but I just don't have the time.

Change 316410 had a related patch set uploaded (by Cenarium):
Notify users of reviews

https://gerrit.wikimedia.org/r/316410

This is what the notification implemented by Cenarium's patch looks like:

Two issues I see with this (I've left comments about these on the Gerrit patch too):

• "Barack Obama" should be bolded, since it's a page name
• The notification should say "edit" or "edits" depending on whether one or multiple edits were approved

In T54510#2875256, @Catrope wrote:

Two issues I see with this (I've left comments about these on the Gerrit patch too):

• "Barack Obama" should be bolded, since it's a page name
• The notification should say "edit" or "edits" depending on whether one or multiple edits were approved

A couple more aspects to consider based on the design guidelines for notifications:

• Remove the "by Admin" part from the message, since the "Admin" user is already captured in the first action. The notification message would be more clear and easier to scan: "Your edits on Barack Obama have been approved."
• The "Help" action seems too generic. If there is a specific kind of information we expect people to look for, it would be good to make it more specific (e.g., "Why is approval needed?", "How review works", etc.). I don't have much context on the purpose for this action and I don't know where the link page points to currently, so take the suggestion with a grain of salt.

I nominated this for the 2019 community wishlist survey (as a volunteer), although it remains to be seen whether it fits the scope.

I've picked this up where @Cenarium left off, rebased into current master and updated some small things to make it work: https://gerrit.wikimedia.org/r/316410/

Looks like this, with the first change suggested by @Pginer-WMF.