sass.js implements a version of Sass much older than the .sass (let alone
currently recommended .scss) described at sass-lang.com, and has poor error
handling so it mostly just ends up confusing users. sass.js's author now uses
stylus/nib. We should probably remove the sass package, but let's not add
another breaking change to 0.5.0.
Meteor's sass package wraps the "sass" NPM module, which implements a version of
the Sass language much older than the .sass described at sass-lang.com (and
doesn't implement the current recommended .scss language at all). It also has
poor error handling, so it mostly just ends up confusing users.
The module is unmaintained, and its author now uses stylus/nib (which Meteor
supports: see the stylus package).
If many users want Sass support, we could add this back in wrapping the
"node-sass" package instead (which supports a more recent version of the Sass
language), but for now, just remove it. Meteor still supports Stylus and Less
out of the box.