@ozh @sam less has the same dependency as grunt (node) but sass has an extra one, ruby. I thought it was hard to set up, but it isn't. In the future (once sasslib is stable) ruby won't be needed. (I don't think core's build is using sasslib yet, I didn't check.)

The build system is node/grunt, which was decided before/independently from the discussion of preprocessors. The choice of less/sass didn't affect the adoption of node/grunt.

The adoption of sass does impact contributors who are working on CSS patches, they'll have to set up node (and ruby in the short term) but it won't affect anyone else. I've tried to make the case that these are fairly entry level requirements for professional frontend devs, so it's not too burdensome.

My general sense of where the lead devs are at, is that if it turns out that installing node/ruby prevents contributions, they might abandon the preprocessor idea.