Considering the proposal to Improve Extension:CSS for Summer_of_Code_2013#Project_ideas... Could we have a reasoning of what needs would this solve in real projects out there? The idea sounds interesting and it is good to see a mentor backing the proposal. The proposal would gain strength if it would be clearer what are the specific problems or limitation MediaWiki sites are facing that would be solved with this project. I get the idea that now they can't use full CSS to style a single page. The question is though who wants to do this and why.
I can see somehow that better per-page CSS capabilities might help building visually attractive wiki pages and follows the line of giving more power to editors as we are doing with templates and gadgets. Still, more feedback from other developers and maintaners would be welcome.
Also more information about the mentor and his involvement in the MediaWiki / Wikimedia community would be welcome. There is not much said in the user profile(s) and I lack more background.