I'm happy to see some research behind what my gut has been sensing for a while. The distinction between "popular" and "popular for new projects" is very important too. Is anyone else talking about whether-or-not this is an active downward trend?
It is interesting to get people who will not support your project if it's CoffeeScript... I would think this is the driving force and not so much that CoffeeScript is not popular.
Besides, I've found that writing CoffeeScript is pretty much like writing Javascript. Different syntax, but the semantics are almost entirely 1:1, leaving out the class stuff (which I don't often use). I've introduced CS to many JS devs and while not all of them loved it, they were able to get up to speed very quickly. But I understand peoples' objections to it - I think they're wrong, but I understand them!
I did make a too quick judgement there. It turns out you can't easily see how popularality of CoffeeScript has changed.
It is surprising to see CoffeeScript in this list as a language compiler
should be mainly a dev-dependency. You compile the CoffeeScript source to
JavaScript for distribution, so you don’t need coffee-script to be a
dependency. The packages that depend upon coffee-script include among others:
grunt, jasmine-node, jscoverage, cucumber and hubot. They all allow you to use
CoffeeScript sources.