The whole point of all chat apps is that you are not physically in the same room already so I'm not sure that we need to be perfectly replicating that. And even so - if you are in a room where you know the person will be returning - you can easily leave a hand written note if you really wanted to.
I am not sure where that quote is from (The point being to isolate sync and async) as I do not see it in the article unless I missed it. I think a lot of this is also indicative of a generational divide - I was an early user of AIM for example and I always remember it being relatively async. There was not a huge expectation that just because you were online and not away that you were always at the computer and constantly replying.
All of this just generally seems like dissatisfaction with the social issues that have developed around all of these technologies in modern times - people EXPECT way too much. Too much is normalized. This is stressing people out. And I think we need to start there to fix it instead of trying to band-aid the problem with tech fix.