So, it is clear that pub/sub on IC opens a whole new world for us. I believe it can simplify integration surface for an infinite amount of different use-cases.
Here is another little rust library from me, that should take pub/sub to a new level introducing on-chain events.
With this library, a canister can become an event-emitter canister, that just shots tons of events without managing where do these events should exactly fly to. Other canisters could become event-listener canisters and to precisely specify which events it wishes to catch and which to skip.
Check it out and let me know what you think.