Anyway, for a server that only does pub/sub with ACID guarantees, those specs are so large that there is certainly a bottleneck before they matter. So it wouldn't be strange if somebody gets one that can't even handle that, it just would mean that there is some issue somewhere we don't see.
In fact, the article makes a very good point how just doing it in postgres is great, it doesn't really scale (because of ACID), and adapting it for scale after you need it will lead to a better design than what you would do if you started optimizing without any information.