Echo only checks revdel/suppression if the notification is revision based (edit-user-talk for example). So...
- Create user "AbusiveUsername"
- Thank "GoodUser" a bunch of times
- Admin hideusers "AbusiveUsername"
- "GoodUser" looks at their notifications and sees "AbusiveUsername" everywhere instead of "username removed"
Hilariously, if you revdel the username from the edit that was thanked (GoodUser's name), Echo will properly display "username removed".
This also works with the user-rights notification type (but that is unlikely to happen practically).
I think the fix here is to check User::isHidden() in addition to the revdel flags?