I guess the main reason to migrate off CoffeeScript is that popular JS tools like for example Serverless Framework do not maintain their CoffeeScript plugins.
I have about 30 old AWS lambdas written in CoffeeScript, which I tried to convert to serverless framework. I tried two serverless-webpack-coffeescript plugins and none of them works. Fixing them requires to know both serverless framework and webpack internals and their plugin APIs are constantly evolving without regard to backward compatibility.
It was much easier to either add a script that runs transpiling before running "serverless deploy" or just to port the source code to JS.
Decaffeinate make this even easier by porting to JS6.