Would it be possible to support CoffeeScript in the Editor? Since it’s CodeMirror then apart from the compilation step (which can be embedded client-side) it should be just about adding coffeescript mode, shouldn’t it? Not sure about the auto-completion though but that’s the killer feature.
CoffeeScript has to be transcompiled into normal JavaScript as browsers don’t do CoffeeScript.
We do not support any other scripting apart of vanilla ES5 JavaScript.
If support will be added to any of languages such as: CoffeeScript, TypeScript, GorillaScript, LiveScript and any other. It will lead to user segregation and separation of knowledge, as not everybody know them. So users won’t be able to learn others code when it is in different languages. Debugging is hard unless you do source maps. Then it will be extra dependency support. And many other less obvious negatives on the community as a whole.
What are benefits? They are very subjective, and opinion based 
This makes sense. Especially after I’ve learned that you guys have CodeMirror integrated with Tern which doesn’t work with transpile-to-js languages so the completion wouldn’t be half as good.