S Page, 11/03/2014 22:19:
"mw" may not need a font stack at all, maybe "the site" here is only WMF properties. Steven Walling, could you clarify the goal?
Periodic reminder: relevant talk page section is https://www.mediawiki.org/wiki/Talk:Typography_refresh#Wikipedia_or_MediaWiki.3F. :)
Nemo