If you're a competent JS programmer you don't need source maps in this case. It's hard to tell from the examples, but it looks like generated JS is not particularly hard to read. Source maps are a must for things like FunScript, js_of_ocaml, Whalesong; they are not very useful in langs like Coffee.

Personally I dislike usage of source maps for Coffee. I want to know what code is being generated. It's good for your health to know this. Most serious C programmers know at least the basics of what asm their compiler generates from which C construct. They can read it (compiled asm) too. I see no reason why this shouldn't be true for Coffee and JS, where it's much, much easier to do anyway.

EDIT: also, as noted by my sibling, it's open source and on Github. You can just go and implement source maps support, I think your pull request would be quickly merged...

Why don't you implement them? Come on!