I uploaded the Agora spec on dropbox[1] to https://www.mediawiki.org/wiki/File:Agora_specs.pdf . I tried to put in appropriate disclaimers and links, edit away.
I filed bug 54360 to implement new Agora spec in the mediawiki.ui CSS module. Now that the LESS CSS preprocessor[2] is in core there's some interest from various engineers. I work on it and a Special:Agora sample page after hours, but it's slow going.
[1] https://www.dropbox.com/s/wa9uayq9j09agyh/Agora%20specs.pdf , from August 20. [2] http://lesscss.org/
Cheers,