Understanding the limitations of Pubsub systems

Finally someone who spells it out. Intuitively, all of this is obvious from the first second you use pubsub systems, the whole "well the messages probably arrive, let's ignore all the distributed systems problems"-thinking and flakiness. But now I have a paper to point to that is pretty well-written.

Pubsub’s first limitation is a Kafka-esque interpretation of "decoupling".

Now I'm wondering how many more of these I missed.