If user pings some bot account, then show the notification for bot operator, because some unexperienced users doesn't know this whole system of bots etc. And I suppose bot operators doesn't frequently log-in their bot accounts (in Wikipedia).
This could be made for DOPPELGANGER accounts.
Also (not mentioned in original talk) was thinking, that this would be useful for WMF people, who have WMF and their personal account.
How this propably could be made? In each user preferences in the Echo part there could be a window, where user could list all those usernames, which pings he/she wants to receive. A little extension to this idea (maybe it is a terrible idea): enable option to receive notifications for unlimited number of users. I think there could be some use cases, when this would be helpful.