I think if we want to use language we should know what we are talking about. I understand his point to be: people have differing opinions of what asynchronous communication (back in the day it was called asynchronous I/O) means, so let's not use the word at all. Instead just describe what you are doing which more words, which are needed anyway and drop the word asynchronous.

I think it is a good idea to give this topic some attention, but I think it is defeatist to conclude that the word is doomed to be useless.

I don't think the communication protocol between two processes, services, whatever has have the property of being synchronous or asynchronous.

It is more about how each side of the communication handles it internally. Synchronous means I shoot off the message, wait until it is processed and I got a response (in case there is supposed to be a response), doing nothing else in the meantime and only after everything is done continue with the next thing I need to do. Asynchronous means I continue doing any type of work in the meantime while the message is sent and processed. That usually means anything that doesn't depend on the response.

Note that my communication partner will usually not care/notice if I am doing anything else in the meantime. I am saying usually because he might notice if I continue sending the same communication partner additional messages before I got a response.

Now the reason why we talk about synchronous and asynchronous communication when communicating between people is that some like to invoke a false equivalence. In the person-to-person communication it is fair to say a phone call, meeting, etc. are methods of synchronous communication and email asynchronous communication. This is more a social thing and has to do with the expectation of time for the response. When I speak on the phone, the receiver has to listen, process and understand exactly at the time I am speaking, i.e. synchronously. That need arises from my social expectation that the person is able to respond in some form seconds later (as opposed to hours or days for something like email). It should be clear here that the terms are used in a different sense as also mentioned in the talk, this is about context, which is also clear in the twitter responses he got. We sometimes have arguments when to prefer one over the other in person-to-person cummincation, and then sometimes this false equivalence with sync/async I/O is invoked.