Per ErikM's suggestion, posting it here.
http://graphtest.wmflabs.org/wiki/Main_Page has a preview of the graph extension https://www.mediawiki.org/wiki/Extension:Graph. The extension is already in production, but will only be enabled for private wikis (zero & fundraising) until we resolve security/privacy concerns (almost done), as well as possible performance implications (node js png rendering)
Graph extension uses vega http://trifacta.github.io/vega/ grammar.