Anakin (obvious), basically already there. Just could be much better organized
Messenger (maybe less obvious)
Messages are derived from every other service, what if it just received events and that's what it stored. Then it could derive generic messages from them.
Website Widget
Because it's in my control.
Analytical events like last_seen_url would be good! (however too high of volume)
Tying messages to website widget events
Could get messages streamed from messenger.
Reviews (Review Rocket / Onix)
We don't own the source of truth, we just need to react to what happens on the review websites