Disclaimer: what follows is my personal opinion, I don’t claim it as “objective truth” 
First, on Ruby’s merits, or lack of, as a technology:
I think Ruby (and Rails) is still an outstandingly good platform for web development. Very successful companies are based on it, the community is still awesome, and the ecosystem is large. But wait, isn’t it {slow/not concurrent/too dynamic/etc.}? Yes. Maybe. It depends. And, more importantly, does it really matter that much?
What I mean is, any team is free to evaluate if in their specific case there is a better choice, but Ruby/Rails is still a great general purpose web development platform: you can definitely do better in any specific area, but as a whole Ruby does a very good job. A good general purpose technology is what many, many companies need. Most companies are not Google scale, and most applications do not have to squeeze every last millisecond. Good developers are harder to find and more expensive than servers (and more and more so), so this is a great trade off in many cases.
What happened is that Ruby, after its early years as a “rebel”, finally became “establishment”, and as such we give its qualities for granted and criticize its limits. That’s perfectly fine, it’s in the life cycle of technologies. But let’s not mistake “buzz” or “engagement” for success and adoption. Ruby is doing fine, it’s just not the cool kid on the block anymore, and that has pros and cons.
Now, about the blog post:
I think it is also perfectly ok for technologies to evolve, and to learn from each other. If good ideas spread, we all win. I have mixed feelings about some of the new syntax additions to Ruby, but then again, nobody is forcing me to use them. While I understand some of the points made by the article, I smell a little bit of ego from the author (which is also the author of the very opinionated Rubocop formatter) as a “keeper of good syntax”, as well as a bit of “I told you so” rhetoric. Yes, some syntax changes were tried, and those that generated more confusion than value were removed before the release, is that so wrong? It sounds to me like a honest way to get feedback from early adopters.
In my view, what is happening is that as Ruby is not surfing the hype curve anymore, its not a good community for “celebrities” anymore. Some of them stayed and enjoyed the quieter productivity, some moved on to other communities, some instead are surfing a bit the “not like the good old times anymore” wave.
