I think you and I probably agree that it'd be a bit of a fools errand to try to make Rails apps more asynchronous. Rails works fine, and as a synchronous design it's straightforward to thread.
It was things like the comparison to Node (which I don't use) and the comment about how well async had worked for you in browser js --- which implicitly somewhat demerited serverside async --- that made me think you might have been reaching for something more ambitious with this post.
I explicitly referenced a chat server (lots of concurrent, mostly-idle requests) as a case where I'd personally use an async solution.
There are certainly middle-ground cases where the question is muddier (and more religious, likely), and I just wanted to set the record straight that Rails itself is not really in the middle. I'm glad that you agree :)