Thanks for this! I would like to suggest something though (and of course, since it will take some work, I am also willing to offer my help), wouldn't it be good to also port this into something like the compass 960 and blueprint plugin?
What I mean is to actually make the classes as mixins instead of just translating the css to sass. That way, instead of having to add the .span9 class to your html element, we can use something more descriptive like .main and then add the mixin +span9 to main. I hope I explained it properly. Anyway, it's just a suggestion, and as I said, I am willing to help :)
