It just totally fragments the node developer community.

Imagine the confusion when you're working with or contributing to two different libraries that have different indentation or documentation standards. Now make the language different, and mix and match different syntaxes for different languages. Should modules in JS accept patches in coffee? What about vice versa?

Not to mention that coffeescript then becomes an additional dependency, and while in itself that's not bad, I still consider less unnecessary dependencies a positive aspect to a library/framework.

Edit: Why downvoted? Is this not a valid concern?

Two bits: Not that it isn't really elegant, but the jump from js to coffeescript does not result in a big enough gain for me to want to do it (as opposed to say, the jump from c to python). It foists an extra mental space on my team, as they have to learn to think in both languages, but doesn't give them a different programming environment with different problem solving tools. If we could totally dump js it might be more appealing. As it is, I see coffeescript splitting the js dev community by making code sharing more difficult.