I am formerly a big fan and user of Gephi, so I think graph drawing is "important enough" to deserve its own JavaScript library, which is why I made sigma.js. I know d3.js is already a great tool, but it looked hardcore for me to tweak it to draw graphs on a Canvas element (it is more easy to use SVG elements). And basically, using a Canvas makes it much more scalable.
About the features to come, you can check https://github.com/jacomyal/sigma.js/blob/master/TODO.txt to see what will come soon. Also, of course, don't hesitate to add some ideas you have in that list :)
