Seriously? Debugging in Sass is a no-brainer - it barfs as soon as there's an error and it's blatantly obvious as soon as you load the page, since the relevant errors are splattered all over the the top of the page (this is a good thing).
This proposal by the W3C is definitely not-even-half-baked.
I don't mean debugging in the sense of "there's a compilation error", I mean in the sense of "oh, that box has a blue border? That's wrong- what line did I define that variable on?". As I said, it's not a huge problem right now, but in more complex files it can take time to track down the original definition that led to the CSS you're seeing.
This proposal by the W3C is definitely not-even-half-baked.